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 $57.65   3.412%   $59.617   $59.62   $59.60   $59.60  
  Purchase #2 $128.53   6.749%   $137.2045   $137.20   $137.20   $137.20  
  Purchase #3 $94.68   11.369%   $105.4442   $105.44   $105.45   $105.40  
  Purchase #4 $187.54   8.112%   $202.7532   $202.75   $202.75   $202.80  
  Purchase #5 $141.66   10.156%   $156.047   $156.05   $156.05   $156.00  
  Purchase #6 $140.70   5.583%   $148.5553   $148.56   $148.55   $148.60  
  Purchase #7 $167.52   11.607%   $186.964   $186.96   $186.95   $187.00  
  7 purchase totals = $918.28       $996.5852   $996.58   $996.55   $996.60