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 $90.79   6.435%   $96.6323   $96.63   $96.65   $96.60  
  Purchase #2 $207.61   4.247%   $216.4272   $216.43   $216.45   $216.40  
  Purchase #3 $59.55   6.681%   $63.5285   $63.53   $63.55   $63.50  
  Purchase #4 $8.96   5.285%   $9.4335   $9.43   $9.45   $9.40  
  Purchase #5 $182.43   7.174%   $195.5175   $195.52   $195.50   $195.50  
  Purchase #6 $43.26   4.433%   $45.1777   $45.18   $45.20   $45.20  
  Purchase #7 $82.52   12.421%   $92.7698   $92.77   $92.75   $92.80  
  7 purchase totals = $675.12       $719.4865   $719.49   $719.55   $719.40