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 $69.64   9.258%   $76.0873   $76.09   $76.10   $76.10  
  Purchase #2 $83.54   11.575%   $93.2098   $93.21   $93.20   $93.20  
  Purchase #3 $91.29   7.281%   $97.9368   $97.94   $97.95   $97.90  
  Purchase #4 $70.34   8.783%   $76.518   $76.52   $76.50   $76.50  
  Purchase #5 $23.40   6.472%   $24.9144   $24.91   $24.90   $24.90  
  Purchase #6 $44.51   13.534%   $50.534   $50.53   $50.55   $50.50  
  Purchase #7 $32.47   10.817%   $35.9823   $35.98   $36.00   $36.00  
  7 purchase totals = $415.19       $455.1826   $455.18   $455.20   $455.10