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 $62.66   11.383%   $69.7926   $69.79   $69.80   $69.80  
  Purchase #2 $238.56   3.823%   $247.6801   $247.68   $247.70   $247.70  
  Purchase #3 $26.38   5.534%   $27.8399   $27.84   $27.85   $27.80  
  Purchase #4 $184.49   11.548%   $205.7949   $205.79   $205.80   $205.80  
  Purchase #5 $162.87   3.208%   $168.0949   $168.09   $168.10   $168.10  
  Purchase #6 $93.32   7.838%   $100.6344   $100.63   $100.65   $100.60  
  Purchase #7 $168.60   8.449%   $182.845   $182.85   $182.85   $182.80  
  7 purchase totals = $936.88       $1,002.6818   $1,002.67   $1,002.75   $1,002.60