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 $39.57   11.336%   $44.0557   $44.06   $44.05   $44.10  
  Purchase #2 $152.73   6.802%   $163.1187   $163.12   $163.10   $163.10  
  Purchase #3 $113.80   5.189%   $119.7051   $119.71   $119.70   $119.70  
  Purchase #4 $237.34   9.617%   $260.165   $260.17   $260.15   $260.20  
  Purchase #5 $193.87   9.342%   $211.9813   $211.98   $212.00   $212.00  
  Purchase #6 $110.49   12.269%   $124.046   $124.05   $124.05   $124.00  
  Purchase #7 $243.92   11.247%   $271.3537   $271.35   $271.35   $271.40  
  7 purchase totals = $1,091.72       $1,194.4255   $1,194.44   $1,194.40   $1,194.50