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 $53.35   10.462%   $58.9315   $58.93   $58.95   $58.90  
  Purchase #2 $117.49   10.186%   $129.4575   $129.46   $129.45   $129.50  
  Purchase #3 $193.36   11.390%   $215.3837   $215.38   $215.40   $215.40  
  Purchase #4 $20.43   11.541%   $22.7878   $22.79   $22.80   $22.80  
  Purchase #5 $170.82   6.225%   $181.4535   $181.45   $181.45   $181.50  
  Purchase #6 $123.49   6.621%   $131.6663   $131.67   $131.65   $131.70  
  Purchase #7 $14.41   8.114%   $15.5792   $15.58   $15.60   $15.60  
  7 purchase totals = $693.35       $755.2595   $755.26   $755.30   $755.40