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 $84.96   8.646%   $92.3056   $92.31   $92.30   $92.30  
  Purchase #2 $52.98   6.716%   $56.5381   $56.54   $56.55   $56.50  
  Purchase #3 $214.49   4.764%   $224.7083   $224.71   $224.70   $224.70  
  Purchase #4 $48.35   4.348%   $50.4523   $50.45   $50.45   $50.50  
  Purchase #5 $61.42   11.385%   $68.4127   $68.41   $68.40   $68.40  
  Purchase #6 $201.25   9.742%   $220.8558   $220.86   $220.85   $220.90  
  Purchase #7 $112.93   9.563%   $123.7295   $123.73   $123.75   $123.70  
  7 purchase totals = $776.38       $837.0023   $837.01   $837.00   $837.00