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 $86.28   10.817%   $95.6129   $95.61   $95.60   $95.60  
  Purchase #2 $234.88   9.384%   $256.9211   $256.92   $256.90   $256.90  
  Purchase #3 $227.61   6.415%   $242.2112   $242.21   $242.20   $242.20  
  Purchase #4 $186.67   10.237%   $205.7794   $205.78   $205.80   $205.80  
  Purchase #5 $172.29   12.692%   $194.157   $194.16   $194.15   $194.20  
  Purchase #6 $77.70   10.602%   $85.9378   $85.94   $85.95   $85.90  
  Purchase #7 $224.35   13.436%   $254.4937   $254.49   $254.50   $254.50  
  7 purchase totals = $1,209.78       $1,335.1131   $1,335.11   $1,335.10   $1,335.10