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 $15.74   11.241%   $17.5093   $17.51   $17.50   $17.50  
  Purchase #2 $206.69   7.737%   $222.6816   $222.68   $222.70   $222.70  
  Purchase #3 $174.46   9.594%   $191.1977   $191.20   $191.20   $191.20  
  Purchase #4 $59.89   5.784%   $63.354   $63.35   $63.35   $63.40  
  Purchase #5 $216.73   10.154%   $238.7368   $238.74   $238.75   $238.70  
  Purchase #6 $199.90   3.481%   $206.8585   $206.86   $206.85   $206.90  
  Purchase #7 $65.51   12.345%   $73.5972   $73.60   $73.60   $73.60  
  7 purchase totals = $938.92       $1,013.9351   $1,013.94   $1,013.95   $1,014.00