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 $148.87   6.311%   $158.2652   $158.27   $158.25   $158.30  
  Purchase #2 $94.78   11.483%   $105.6636   $105.66   $105.65   $105.70  
  Purchase #3 $57.59   9.855%   $63.2655   $63.27   $63.25   $63.30  
  Purchase #4 $162.36   4.631%   $169.8789   $169.88   $169.90   $169.90  
  Purchase #5 $47.39   11.251%   $52.7218   $52.72   $52.70   $52.70  
  Purchase #6 $34.50   5.322%   $36.3361   $36.34   $36.35   $36.30  
  Purchase #7 $110.28   10.551%   $121.9156   $121.92   $121.90   $121.90  
  7 purchase totals = $655.77       $708.0467   $708.06   $708.00   $708.10