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 $173.50   12.360%   $194.9446   $194.94   $194.95   $194.90  
  Purchase #2 $244.73   5.102%   $257.2161   $257.22   $257.20   $257.20  
  Purchase #3 $227.33   7.736%   $244.9162   $244.92   $244.90   $244.90  
  Purchase #4 $28.61   5.152%   $30.084   $30.08   $30.10   $30.10  
  Purchase #5 $246.62   12.691%   $277.9185   $277.92   $277.90   $277.90  
  Purchase #6 $246.63   5.699%   $260.6854   $260.69   $260.70   $260.70  
  Purchase #7 $67.47   12.811%   $76.1136   $76.11   $76.10   $76.10  
  7 purchase totals = $1,234.89       $1,341.8784   $1,341.88   $1,341.85   $1,341.80