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 $217.27   11.710%   $242.7123   $242.71   $242.70   $242.70  
  Purchase #2 $41.96   11.697%   $46.8681   $46.87   $46.85   $46.90  
  Purchase #3 $232.37   7.609%   $250.051   $250.05   $250.05   $250.10  
  Purchase #4 $226.36   13.410%   $256.7149   $256.71   $256.70   $256.70  
  Purchase #5 $60.84   9.378%   $66.5456   $66.55   $66.55   $66.50  
  Purchase #6 $119.97   11.293%   $133.5182   $133.52   $133.50   $133.50  
  Purchase #7 $16.78   13.191%   $18.9934   $18.99   $19.00   $19.00  
  7 purchase totals = $915.55       $1,015.4035   $1,015.40   $1,015.35   $1,015.40