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 $73.54   13.782%   $83.6753   $83.68   $83.70   $83.70  
  Purchase #2 $43.78   5.227%   $46.0684   $46.07   $46.05   $46.10  
  Purchase #3 $24.25   5.684%   $25.6284   $25.63   $25.65   $25.60  
  Purchase #4 $232.98   3.739%   $241.6911   $241.69   $241.70   $241.70  
  Purchase #5 $156.27   6.259%   $166.0509   $166.05   $166.05   $166.10  
  Purchase #6 $207.77   10.602%   $229.7978   $229.80   $229.80   $229.80  
  Purchase #7 $103.35   4.825%   $108.3366   $108.34   $108.35   $108.30  
  7 purchase totals = $841.94       $901.2485   $901.26   $901.30   $901.30