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 $65.82   4.180%   $68.5713   $68.57   $68.55   $68.60  
  Purchase #2 $201.58   13.428%   $228.6482   $228.65   $228.65   $228.60  
  Purchase #3 $91.96   7.444%   $98.8055   $98.81   $98.80   $98.80  
  Purchase #4 $187.37   7.395%   $201.226   $201.23   $201.25   $201.20  
  Purchase #5 $248.59   5.776%   $262.9486   $262.95   $262.95   $262.90  
  Purchase #6 $55.26   13.559%   $62.7527   $62.75   $62.75   $62.80  
  Purchase #7 $22.27   3.116%   $22.9639   $22.96   $22.95   $23.00  
  7 purchase totals = $872.85       $945.9162   $945.92   $945.90   $945.90