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 $151.27   8.853%   $164.6619   $164.66   $164.65   $164.70  
  Purchase #2 $244.48   10.469%   $270.0746   $270.07   $270.05   $270.10  
  Purchase #3 $84.77   6.561%   $90.3318   $90.33   $90.35   $90.30  
  Purchase #4 $166.44   4.374%   $173.7201   $173.72   $173.70   $173.70  
  Purchase #5 $106.66   6.451%   $113.5406   $113.54   $113.55   $113.50  
  Purchase #6 $132.34   10.331%   $146.012   $146.01   $146.00   $146.00  
  Purchase #7 $62.96   4.341%   $65.6931   $65.69   $65.70   $65.70  
  7 purchase totals = $948.92       $1,024.0341   $1,024.02   $1,024.00   $1,024.00