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 $239.66   12.427%   $269.4425   $269.44   $269.45   $269.40  
  Purchase #2 $20.28   11.325%   $22.5767   $22.58   $22.60   $22.60  
  Purchase #3 $203.50   13.588%   $231.1516   $231.15   $231.15   $231.20  
  Purchase #4 $60.94   8.779%   $66.2899   $66.29   $66.30   $66.30  
  Purchase #5 $232.85   5.425%   $245.4821   $245.48   $245.50   $245.50  
  Purchase #6 $39.51   11.332%   $43.9873   $43.99   $44.00   $44.00  
  Purchase #7 $196.58   11.534%   $219.2535   $219.25   $219.25   $219.30  
  7 purchase totals = $993.32       $1,098.1836   $1,098.18   $1,098.25   $1,098.30