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 $76.54   9.439%   $83.7646   $83.76   $83.75   $83.80  
  Purchase #2 $202.63   4.503%   $211.7544   $211.75   $211.75   $211.80  
  Purchase #3 $45.30   9.296%   $49.5111   $49.51   $49.50   $49.50  
  Purchase #4 $238.65   5.401%   $251.5395   $251.54   $251.55   $251.50  
  Purchase #5 $144.68   4.137%   $150.6654   $150.67   $150.65   $150.70  
  Purchase #6 $210.42   3.651%   $218.1024   $218.10   $218.10   $218.10  
  Purchase #7 $160.73   4.295%   $167.6334   $167.63   $167.65   $167.60  
  7 purchase totals = $1,078.95       $1,132.9708   $1,132.96   $1,132.95   $1,133.00