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 $67.25   11.213%   $74.7907   $74.79   $74.80   $74.80  
  Purchase #2 $232.93   11.778%   $260.3645   $260.36   $260.35   $260.40  
  Purchase #3 $162.28   5.757%   $171.6225   $171.62   $171.60   $171.60  
  Purchase #4 $241.41   4.492%   $252.2541   $252.25   $252.25   $252.30  
  Purchase #5 $207.80   7.177%   $222.7138   $222.71   $222.70   $222.70  
  Purchase #6 $222.68   7.116%   $238.5259   $238.53   $238.55   $238.50  
  Purchase #7 $61.55   5.738%   $65.0817   $65.08   $65.10   $65.10  
  7 purchase totals = $1,195.90       $1,285.3532   $1,285.34   $1,285.35   $1,285.40