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 $205.87   12.714%   $232.0443   $232.04   $232.05   $232.00  
  Purchase #2 $225.62   8.266%   $244.2697   $244.27   $244.25   $244.30  
  Purchase #3 $189.56   3.583%   $196.3519   $196.35   $196.35   $196.40  
  Purchase #4 $188.83   3.281%   $195.0255   $195.03   $195.05   $195.00  
  Purchase #5 $171.43   3.181%   $176.8832   $176.88   $176.90   $176.90  
  Purchase #6 $86.86   5.868%   $91.9569   $91.96   $91.95   $92.00  
  Purchase #7 $98.88   6.620%   $105.4259   $105.43   $105.45   $105.40  
  7 purchase totals = $1,167.05       $1,241.9574   $1,241.96   $1,242.00   $1,242.00