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 $92.29   3.848%   $95.8413   $95.84   $95.85   $95.80  
  Purchase #2 $219.28   12.812%   $247.3742   $247.37   $247.35   $247.40  
  Purchase #3 $203.77   7.610%   $219.2769   $219.28   $219.30   $219.30  
  Purchase #4 $241.54   11.550%   $269.4379   $269.44   $269.45   $269.40  
  Purchase #5 $23.77   12.520%   $26.746   $26.75   $26.75   $26.70  
  Purchase #6 $159.78   3.776%   $165.8133   $165.81   $165.80   $165.80  
  Purchase #7 $230.73   4.863%   $241.9504   $241.95   $241.95   $242.00  
  7 purchase totals = $1,171.16       $1,266.4400   $1,266.44   $1,266.45   $1,266.40