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 $180.73   7.467%   $194.2251   $194.23   $194.25   $194.20  
  Purchase #2 $250.94   3.462%   $259.6275   $259.63   $259.65   $259.60  
  Purchase #3 $128.27   8.150%   $138.724   $138.72   $138.70   $138.70  
  Purchase #4 $122.29   6.793%   $130.5972   $130.60   $130.60   $130.60  
  Purchase #5 $208.75   3.284%   $215.6054   $215.61   $215.60   $215.60  
  Purchase #6 $61.65   5.767%   $65.2054   $65.21   $65.20   $65.20  
  Purchase #7 $221.56   9.766%   $243.1975   $243.20   $243.20   $243.20  
  7 purchase totals = $1,174.19       $1,247.1821   $1,247.20   $1,247.20   $1,247.10