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 $67.77   12.141%   $75.998   $76.00   $76.00   $76.00  
  Purchase #2 $213.48   3.127%   $220.1555   $220.16   $220.15   $220.20  
  Purchase #3 $42.47   11.222%   $47.236   $47.24   $47.25   $47.20  
  Purchase #4 $46.62   10.658%   $51.5888   $51.59   $51.60   $51.60  
  Purchase #5 $55.28   7.686%   $59.5288   $59.53   $59.55   $59.50  
  Purchase #6 $217.46   3.735%   $225.5821   $225.58   $225.60   $225.60  
  Purchase #7 $237.30   3.521%   $245.6553   $245.66   $245.65   $245.70  
  7 purchase totals = $880.38       $925.7445   $925.76   $925.80   $925.80