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 $45.27   12.477%   $50.9183   $50.92   $50.90   $50.90  
  Purchase #2 $62.36   9.519%   $68.296   $68.30   $68.30   $68.30  
  Purchase #3 $213.46   6.695%   $227.7511   $227.75   $227.75   $227.80  
  Purchase #4 $167.89   3.411%   $173.6167   $173.62   $173.60   $173.60  
  Purchase #5 $246.26   10.781%   $272.8093   $272.81   $272.80   $272.80  
  Purchase #6 $240.46   8.481%   $260.8534   $260.85   $260.85   $260.90  
  Purchase #7 $208.75   8.585%   $226.6712   $226.67   $226.65   $226.70  
  7 purchase totals = $1,184.45       $1,280.9160   $1,280.92   $1,280.85   $1,281.00