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 $52.26   7.719%   $56.2939   $56.29   $56.30   $56.30  
  Purchase #2 $99.35   11.865%   $111.1379   $111.14   $111.15   $111.10  
  Purchase #3 $38.74   8.270%   $41.9438   $41.94   $41.95   $41.90  
  Purchase #4 $195.31   5.656%   $206.3567   $206.36   $206.35   $206.40  
  Purchase #5 $218.41   4.367%   $227.948   $227.95   $227.95   $227.90  
  Purchase #6 $155.78   9.695%   $170.8829   $170.88   $170.90   $170.90  
  Purchase #7 $139.64   8.684%   $151.7663   $151.77   $151.75   $151.80  
  7 purchase totals = $899.49       $966.3295   $966.33   $966.35   $966.30