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 $68.94   9.442%   $75.4493   $75.45   $75.45   $75.40  
  Purchase #2 $114.72   5.121%   $120.5948   $120.59   $120.60   $120.60  
  Purchase #3 $139.59   12.627%   $157.216   $157.22   $157.20   $157.20  
  Purchase #4 $227.53   11.181%   $252.9701   $252.97   $252.95   $253.00  
  Purchase #5 $118.91   4.414%   $124.1587   $124.16   $124.15   $124.20  
  Purchase #6 $25.91   6.460%   $27.5838   $27.58   $27.60   $27.60  
  Purchase #7 $64.63   3.566%   $66.9347   $66.93   $66.95   $66.90  
  7 purchase totals = $760.23       $824.9074   $824.90   $824.90   $824.90