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 $241.76   9.647%   $265.0826   $265.08   $265.10   $265.10  
  Purchase #2 $140.80   13.450%   $159.7376   $159.74   $159.75   $159.70  
  Purchase #3 $219.49   8.318%   $237.7472   $237.75   $237.75   $237.70  
  Purchase #4 $224.80   3.366%   $232.3668   $232.37   $232.35   $232.40  
  Purchase #5 $206.53   9.683%   $226.5283   $226.53   $226.55   $226.50  
  Purchase #6 $138.76   11.248%   $154.3677   $154.37   $154.35   $154.40  
  Purchase #7 $234.34   5.237%   $246.6124   $246.61   $246.60   $246.60  
  7 purchase totals = $1,406.48       $1,522.4426   $1,522.45   $1,522.45   $1,522.40