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 $29.61   13.874%   $33.7181   $33.72   $33.70   $33.70  
  Purchase #2 $163.28   9.418%   $178.6577   $178.66   $178.65   $178.70  
  Purchase #3 $165.31   11.170%   $183.7751   $183.78   $183.80   $183.80  
  Purchase #4 $127.95   5.799%   $135.3698   $135.37   $135.35   $135.40  
  Purchase #5 $205.73   9.837%   $225.9677   $225.97   $225.95   $226.00  
  Purchase #6 $69.67   13.241%   $78.895   $78.90   $78.90   $78.90  
  Purchase #7 $13.89   11.182%   $15.4432   $15.44   $15.45   $15.40  
  7 purchase totals = $775.44       $851.8266   $851.84   $851.80   $851.90