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 $241.98   3.359%   $250.1081   $250.11   $250.10   $250.10  
  Purchase #2 $13.81   11.204%   $15.3573   $15.36   $15.35   $15.40  
  Purchase #3 $75.35   12.511%   $84.777   $84.78   $84.80   $84.80  
  Purchase #4 $62.48   10.206%   $68.8567   $68.86   $68.85   $68.90  
  Purchase #5 $209.49   5.418%   $220.8402   $220.84   $220.85   $220.80  
  Purchase #6 $220.72   5.304%   $232.427   $232.43   $232.45   $232.40  
  Purchase #7 $215.97   3.668%   $223.8918   $223.89   $223.90   $223.90  
  7 purchase totals = $1,039.80       $1,096.2581   $1,096.27   $1,096.30   $1,096.30