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 $175.26   12.121%   $196.5033   $196.50   $196.50   $196.50  
  Purchase #2 $250.88   12.258%   $281.6329   $281.63   $281.65   $281.60  
  Purchase #3 $22.62   8.255%   $24.4873   $24.49   $24.50   $24.50  
  Purchase #4 $250.62   4.850%   $262.7751   $262.78   $262.80   $262.80  
  Purchase #5 $157.60   13.516%   $178.9012   $178.90   $178.90   $178.90  
  Purchase #6 $121.43   8.699%   $131.9932   $131.99   $132.00   $132.00  
  Purchase #7 $180.78   7.343%   $194.0547   $194.05   $194.05   $194.10  
  7 purchase totals = $1,159.19       $1,270.3477   $1,270.34   $1,270.40   $1,270.40