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 $83.83   10.411%   $92.5575   $92.56   $92.55   $92.60  
  Purchase #2 $79.49   4.385%   $82.9756   $82.98   $83.00   $83.00  
  Purchase #3 $182.59   11.816%   $204.1648   $204.16   $204.15   $204.20  
  Purchase #4 $188.59   8.530%   $204.6767   $204.68   $204.70   $204.70  
  Purchase #5 $45.68   12.418%   $51.3525   $51.35   $51.35   $51.40  
  Purchase #6 $123.92   3.719%   $128.5286   $128.53   $128.55   $128.50  
  Purchase #7 $27.70   4.236%   $28.8734   $28.87   $28.85   $28.90  
  7 purchase totals = $731.80       $793.1291   $793.13   $793.15   $793.30