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 $154.77   12.819%   $174.61   $174.61   $174.60   $174.60  
  Purchase #2 $10.94   5.563%   $11.5486   $11.55   $11.55   $11.50  
  Purchase #3 $146.44   10.568%   $161.9158   $161.92   $161.90   $161.90  
  Purchase #4 $242.94   5.411%   $256.0855   $256.09   $256.10   $256.10  
  Purchase #5 $28.84   6.582%   $30.7382   $30.74   $30.75   $30.70  
  Purchase #6 $125.94   5.252%   $132.5544   $132.55   $132.55   $132.60  
  Purchase #7 $236.73   6.334%   $251.7245   $251.72   $251.70   $251.70  
  7 purchase totals = $946.60       $1,019.1770   $1,019.18   $1,019.15   $1,019.10