Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $230.44   13.224%   $260.9134   $260.91   $260.90   $260.90  
  Purchase #2 $116.85   11.489%   $130.2749   $130.27   $130.25   $130.30  
  Purchase #3 $140.96   11.272%   $156.849   $156.85   $156.85   $156.80  
  Purchase #4 $236.98   4.476%   $247.5872   $247.59   $247.60   $247.60  
  Purchase #5 $94.34   11.427%   $105.1202   $105.12   $105.10   $105.10  
  Purchase #6 $230.90   9.372%   $252.5399   $252.54   $252.55   $252.50  
  Purchase #7 $203.66   6.548%   $216.9957   $217.00   $217.00   $217.00  
  7 purchase totals = $1,254.13       $1,370.2803   $1,370.28   $1,370.25   $1,370.20