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 $56.61   8.836%   $61.6121   $61.61   $61.60   $61.60  
  Purchase #2 $86.53   5.746%   $91.502   $91.50   $91.50   $91.50  
  Purchase #3 $229.38   5.338%   $241.6243   $241.62   $241.60   $241.60  
  Purchase #4 $15.77   12.269%   $17.7048   $17.70   $17.70   $17.70  
  Purchase #5 $84.49   12.435%   $94.9963   $95.00   $95.00   $95.00  
  Purchase #6 $92.79   12.114%   $104.0306   $104.03   $104.05   $104.00  
  Purchase #7 $165.35   3.772%   $171.587   $171.59   $171.60   $171.60  
  7 purchase totals = $730.92       $783.0571   $783.05   $783.05   $783.00