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 $51.41   9.414%   $56.2497   $56.25   $56.25   $56.20  
  Purchase #2 $230.50   13.180%   $260.8799   $260.88   $260.90   $260.90  
  Purchase #3 $219.80   4.202%   $229.036   $229.04   $229.05   $229.00  
  Purchase #4 $162.80   5.360%   $171.5261   $171.53   $171.55   $171.50  
  Purchase #5 $86.34   12.647%   $97.2594   $97.26   $97.25   $97.30  
  Purchase #6 $111.30   12.614%   $125.3394   $125.34   $125.35   $125.30  
  Purchase #7 $202.62   7.267%   $217.3444   $217.34   $217.35   $217.30  
  7 purchase totals = $1,064.77       $1,157.6349   $1,157.64   $1,157.70   $1,157.50