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 $204.62   13.336%   $231.9081   $231.91   $231.90   $231.90  
  Purchase #2 $217.49   9.830%   $238.8693   $238.87   $238.85   $238.90  
  Purchase #3 $169.94   5.387%   $179.0947   $179.09   $179.10   $179.10  
  Purchase #4 $183.32   5.399%   $193.2174   $193.22   $193.20   $193.20  
  Purchase #5 $110.51   8.258%   $119.6359   $119.64   $119.65   $119.60  
  Purchase #6 $225.59   13.615%   $256.3041   $256.30   $256.30   $256.30  
  Purchase #7 $48.29   13.169%   $54.6493   $54.65   $54.65   $54.60  
  7 purchase totals = $1,159.76       $1,273.6788   $1,273.68   $1,273.65   $1,273.60