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 $48.89   11.836%   $54.6766   $54.68   $54.70   $54.70  
  Purchase #2 $223.48   6.453%   $237.9012   $237.90   $237.90   $237.90  
  Purchase #3 $90.98   3.556%   $94.2152   $94.22   $94.20   $94.20  
  Purchase #4 $130.76   9.565%   $143.2672   $143.27   $143.25   $143.30  
  Purchase #5 $63.74   8.221%   $68.9801   $68.98   $69.00   $69.00  
  Purchase #6 $143.81   10.207%   $158.4887   $158.49   $158.50   $158.50  
  Purchase #7 $62.61   10.788%   $69.3644   $69.36   $69.35   $69.40  
  7 purchase totals = $764.27       $826.8934   $826.90   $826.90   $827.00