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 $51.43   10.326%   $56.7407   $56.74   $56.75   $56.70  
  Purchase #2 $32.36   11.109%   $35.9549   $35.95   $35.95   $36.00  
  Purchase #3 $166.29   6.399%   $176.9309   $176.93   $176.95   $176.90  
  Purchase #4 $39.90   6.803%   $42.6144   $42.61   $42.60   $42.60  
  Purchase #5 $195.53   4.471%   $204.2721   $204.27   $204.25   $204.30  
  Purchase #6 $94.28   13.192%   $106.7174   $106.72   $106.70   $106.70  
  Purchase #7 $48.65   8.407%   $52.74   $52.74   $52.75   $52.70  
  7 purchase totals = $628.44       $675.9704   $675.96   $675.95   $675.90