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 $209.49   11.312%   $233.1875   $233.19   $233.20   $233.20  
  Purchase #2 $200.91   13.489%   $228.0107   $228.01   $228.00   $228.00  
  Purchase #3 $148.80   13.844%   $169.3999   $169.40   $169.40   $169.40  
  Purchase #4 $30.87   10.106%   $33.9897   $33.99   $34.00   $34.00  
  Purchase #5 $217.55   12.847%   $245.4986   $245.50   $245.50   $245.50  
  Purchase #6 $5.44   12.120%   $6.0993   $6.10   $6.10   $6.10  
  Purchase #7 $25.81   10.275%   $28.462   $28.46   $28.45   $28.50  
  7 purchase totals = $838.87       $944.6477   $944.65   $944.65   $944.70