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 $82.86   12.754%   $93.428   $93.43   $93.45   $93.40  
  Purchase #2 $30.36   11.440%   $33.8332   $33.83   $33.85   $33.80  
  Purchase #3 $142.90   5.594%   $150.8938   $150.89   $150.90   $150.90  
  Purchase #4 $129.69   3.704%   $134.4937   $134.49   $134.50   $134.50  
  Purchase #5 $29.54   11.153%   $32.8346   $32.83   $32.85   $32.80  
  Purchase #6 $197.70   3.396%   $204.4139   $204.41   $204.40   $204.40  
  Purchase #7 $70.44   6.341%   $74.9066   $74.91   $74.90   $74.90  
  7 purchase totals = $683.49       $724.8038   $724.79   $724.85   $724.70