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 $91.80   5.582%   $96.9243   $96.92   $96.90   $96.90  
  Purchase #2 $192.27   5.237%   $202.3392   $202.34   $202.35   $202.30  
  Purchase #3 $10.53   8.293%   $11.4033   $11.40   $11.40   $11.40  
  Purchase #4 $91.74   6.423%   $97.6325   $97.63   $97.65   $97.60  
  Purchase #5 $162.49   5.413%   $171.2856   $171.29   $171.30   $171.30  
  Purchase #6 $57.95   10.428%   $63.993   $63.99   $64.00   $64.00  
  Purchase #7 $249.73   10.827%   $276.7683   $276.77   $276.75   $276.80  
  7 purchase totals = $856.51       $920.3462   $920.34   $920.35   $920.30