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 $156.69   8.226%   $169.5793   $169.58   $169.60   $169.60  
  Purchase #2 $90.89   13.542%   $103.1983   $103.20   $103.20   $103.20  
  Purchase #3 $156.73   10.691%   $173.486   $173.49   $173.50   $173.50  
  Purchase #4 $44.49   8.722%   $48.3704   $48.37   $48.35   $48.40  
  Purchase #5 $6.49   5.133%   $6.8231   $6.82   $6.80   $6.80  
  Purchase #6 $232.45   6.310%   $247.1176   $247.12   $247.10   $247.10  
  Purchase #7 $98.57   6.226%   $104.707   $104.71   $104.70   $104.70  
  7 purchase totals = $786.31       $853.2817   $853.29   $853.25   $853.30