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 $55.34   10.822%   $61.3289   $61.33   $61.35   $61.30  
  Purchase #2 $142.88   7.574%   $153.7017   $153.70   $153.70   $153.70  
  Purchase #3 $73.89   5.387%   $77.8705   $77.87   $77.85   $77.90  
  Purchase #4 $161.30   5.138%   $169.5876   $169.59   $169.60   $169.60  
  Purchase #5 $171.39   13.797%   $195.0367   $195.04   $195.05   $195.00  
  Purchase #6 $56.38   11.805%   $63.0357   $63.04   $63.05   $63.00  
  Purchase #7 $145.71   7.285%   $156.325   $156.33   $156.35   $156.30  
  7 purchase totals = $806.89       $876.8861   $876.90   $876.95   $876.80