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 $148.76   13.864%   $169.3841   $169.38   $169.40   $169.40  
  Purchase #2 $166.93   9.828%   $183.3359   $183.34   $183.35   $183.30  
  Purchase #3 $166.29   4.436%   $173.6666   $173.67   $173.65   $173.70  
  Purchase #4 $48.37   12.154%   $54.2489   $54.25   $54.25   $54.20  
  Purchase #5 $45.88   7.647%   $49.3884   $49.39   $49.40   $49.40  
  Purchase #6 $226.71   7.559%   $243.847   $243.85   $243.85   $243.80  
  Purchase #7 $151.99   8.497%   $164.9046   $164.90   $164.90   $164.90  
  7 purchase totals = $954.93       $1,038.7755   $1,038.78   $1,038.80   $1,038.70