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 $185.90   9.314%   $203.2147   $203.21   $203.20   $203.20  
  Purchase #2 $66.65   7.484%   $71.6381   $71.64   $71.65   $71.60  
  Purchase #3 $221.76   8.565%   $240.7537   $240.75   $240.75   $240.80  
  Purchase #4 $108.65   4.335%   $113.36   $113.36   $113.35   $113.40  
  Purchase #5 $24.67   11.234%   $27.4414   $27.44   $27.45   $27.40  
  Purchase #6 $234.54   11.583%   $261.7068   $261.71   $261.70   $261.70  
  Purchase #7 $94.86   13.207%   $107.3882   $107.39   $107.40   $107.40  
  7 purchase totals = $937.03       $1,025.5029   $1,025.50   $1,025.50   $1,025.50