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 $169.59   13.201%   $191.9776   $191.98   $192.00   $192.00  
  Purchase #2 $108.54   7.749%   $116.9508   $116.95   $116.95   $117.00  
  Purchase #3 $205.40   11.185%   $228.374   $228.37   $228.35   $228.40  
  Purchase #4 $115.40   3.557%   $119.5048   $119.50   $119.50   $119.50  
  Purchase #5 $133.90   10.737%   $148.2768   $148.28   $148.30   $148.30  
  Purchase #6 $10.65   10.759%   $11.7958   $11.80   $11.80   $11.80  
  Purchase #7 $62.78   7.252%   $67.3328   $67.33   $67.35   $67.30  
  7 purchase totals = $806.26       $884.2126   $884.21   $884.25   $884.30