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 $34.83   3.241%   $35.9588   $35.96   $35.95   $36.00  
  Purchase #2 $41.78   12.813%   $47.1333   $47.13   $47.15   $47.10  
  Purchase #3 $238.57   11.203%   $265.297   $265.30   $265.30   $265.30  
  Purchase #4 $59.46   3.277%   $61.4085   $61.41   $61.40   $61.40  
  Purchase #5 $243.68   13.283%   $276.048   $276.05   $276.05   $276.00  
  Purchase #6 $151.38   11.336%   $168.5404   $168.54   $168.55   $168.50  
  Purchase #7 $64.55   6.572%   $68.7922   $68.79   $68.80   $68.80  
  7 purchase totals = $834.25       $923.1782   $923.18   $923.20   $923.10