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 $70.40   4.273%   $73.4082   $73.41   $73.40   $73.40  
  Purchase #2 $19.78   8.743%   $21.5094   $21.51   $21.50   $21.50  
  Purchase #3 $185.42   8.588%   $201.3439   $201.34   $201.35   $201.30  
  Purchase #4 $122.26   5.678%   $129.2019   $129.20   $129.20   $129.20  
  Purchase #5 $117.84   9.701%   $129.2717   $129.27   $129.25   $129.30  
  Purchase #6 $27.59   4.351%   $28.7904   $28.79   $28.80   $28.80  
  Purchase #7 $37.53   4.581%   $39.2492   $39.25   $39.25   $39.20  
  7 purchase totals = $580.82       $622.7747   $622.77   $622.75   $622.70