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 $188.98   6.485%   $201.2354   $201.24   $201.25   $201.20  
  Purchase #2 $94.56   8.607%   $102.6988   $102.70   $102.70   $102.70  
  Purchase #3 $61.25   3.556%   $63.4281   $63.43   $63.45   $63.40  
  Purchase #4 $70.87   6.656%   $75.5871   $75.59   $75.60   $75.60  
  Purchase #5 $75.55   4.374%   $78.8546   $78.85   $78.85   $78.90  
  Purchase #6 $98.93   4.307%   $103.1909   $103.19   $103.20   $103.20  
  Purchase #7 $165.56   12.568%   $186.3676   $186.37   $186.35   $186.40  
  7 purchase totals = $755.70       $811.3625   $811.37   $811.40   $811.40