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 $104.86   13.150%   $118.6491   $118.65   $118.65   $118.60  
  Purchase #2 $224.74   4.715%   $235.3365   $235.34   $235.35   $235.30  
  Purchase #3 $75.66   5.340%   $79.7002   $79.70   $79.70   $79.70  
  Purchase #4 $113.39   3.633%   $117.5095   $117.51   $117.50   $117.50  
  Purchase #5 $71.72   7.239%   $76.9118   $76.91   $76.90   $76.90  
  Purchase #6 $45.26   10.626%   $50.0693   $50.07   $50.05   $50.10  
  Purchase #7 $90.49   6.196%   $96.0968   $96.10   $96.10   $96.10  
  7 purchase totals = $726.12       $774.2732   $774.28   $774.25   $774.20