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 $194.63   5.508%   $205.3502   $205.35   $205.35   $205.40  
  Purchase #2 $116.92   4.275%   $121.9183   $121.92   $121.90   $121.90  
  Purchase #3 $240.56   5.526%   $253.8533   $253.85   $253.85   $253.90  
  Purchase #4 $23.36   3.663%   $24.2157   $24.22   $24.20   $24.20  
  Purchase #5 $227.70   6.644%   $242.8284   $242.83   $242.85   $242.80  
  Purchase #6 $49.78   4.310%   $51.9255   $51.93   $51.95   $51.90  
  Purchase #7 $45.74   5.634%   $48.317   $48.32   $48.30   $48.30  
  7 purchase totals = $898.69       $948.4084   $948.42   $948.40   $948.40