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 $88.53   4.771%   $92.7538   $92.75   $92.75   $92.80  
  Purchase #2 $248.49   4.325%   $259.2372   $259.24   $259.25   $259.20  
  Purchase #3 $206.45   9.799%   $226.68   $226.68   $226.70   $226.70  
  Purchase #4 $169.34   10.560%   $187.2223   $187.22   $187.20   $187.20  
  Purchase #5 $250.95   6.573%   $267.4449   $267.44   $267.45   $267.40  
  Purchase #6 $18.31   9.289%   $20.0108   $20.01   $20.00   $20.00  
  Purchase #7 $172.95   13.446%   $196.2049   $196.20   $196.20   $196.20  
  7 purchase totals = $1,155.02       $1,249.5539   $1,249.54   $1,249.55   $1,249.50