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 $104.65   10.272%   $115.3996   $115.40   $115.40   $115.40  
  Purchase #2 $189.95   7.399%   $204.0044   $204.00   $204.00   $204.00  
  Purchase #3 $210.28   5.870%   $222.6234   $222.62   $222.60   $222.60  
  Purchase #4 $84.44   13.135%   $95.5312   $95.53   $95.55   $95.50  
  Purchase #5 $225.25   6.859%   $240.6999   $240.70   $240.70   $240.70  
  Purchase #6 $211.27   12.607%   $237.9048   $237.90   $237.90   $237.90  
  Purchase #7 $199.44   13.575%   $226.514   $226.51   $226.50   $226.50  
  7 purchase totals = $1,225.28       $1,342.6773   $1,342.66   $1,342.65   $1,342.60