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 $60.41   12.442%   $67.9262   $67.93   $67.95   $67.90  
  Purchase #2 $238.98   8.772%   $259.9433   $259.94   $259.95   $259.90  
  Purchase #3 $173.85   6.159%   $184.5574   $184.56   $184.55   $184.60  
  Purchase #4 $224.50   3.389%   $232.1083   $232.11   $232.10   $232.10  
  Purchase #5 $88.73   11.237%   $98.7006   $98.70   $98.70   $98.70  
  Purchase #6 $218.87   7.804%   $235.9506   $235.95   $235.95   $236.00  
  Purchase #7 $235.56   13.177%   $266.5997   $266.60   $266.60   $266.60  
  7 purchase totals = $1,240.90       $1,345.7861   $1,345.79   $1,345.80   $1,345.80