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 $56.79   9.689%   $62.2924   $62.29   $62.30   $62.30  
  Purchase #2 $189.39   4.262%   $197.4618   $197.46   $197.45   $197.50  
  Purchase #3 $100.53   5.421%   $105.9797   $105.98   $106.00   $106.00  
  Purchase #4 $204.46   13.819%   $232.7143   $232.71   $232.70   $232.70  
  Purchase #5 $209.82   10.676%   $232.2204   $232.22   $232.20   $232.20  
  Purchase #6 $77.71   10.648%   $85.9846   $85.98   $86.00   $86.00  
  Purchase #7 $74.59   6.559%   $79.4824   $79.48   $79.50   $79.50  
  7 purchase totals = $913.29       $996.1356   $996.12   $996.15   $996.20