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 $126.27   6.265%   $134.1808   $134.18   $134.20   $134.20  
  Purchase #2 $40.48   3.833%   $42.0316   $42.03   $42.05   $42.00  
  Purchase #3 $54.78   13.118%   $61.966   $61.97   $61.95   $62.00  
  Purchase #4 $213.49   10.243%   $235.3578   $235.36   $235.35   $235.40  
  Purchase #5 $183.53   10.662%   $203.098   $203.10   $203.10   $203.10  
  Purchase #6 $59.97   13.606%   $68.1295   $68.13   $68.15   $68.10  
  Purchase #7 $156.25   11.671%   $174.4859   $174.49   $174.50   $174.50  
  7 purchase totals = $834.77       $919.2496   $919.26   $919.30   $919.30