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 $75.33   4.363%   $78.6166   $78.62   $78.60   $78.60  
  Purchase #2 $78.65   9.374%   $86.0227   $86.02   $86.00   $86.00  
  Purchase #3 $86.61   12.141%   $97.1253   $97.13   $97.15   $97.10  
  Purchase #4 $67.95   13.352%   $77.0227   $77.02   $77.00   $77.00  
  Purchase #5 $119.26   4.193%   $124.2606   $124.26   $124.25   $124.30  
  Purchase #6 $109.87   6.726%   $117.2599   $117.26   $117.25   $117.30  
  Purchase #7 $201.64   4.295%   $210.3004   $210.30   $210.30   $210.30  
  7 purchase totals = $739.31       $790.6082   $790.61   $790.55   $790.60