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 $79.82   6.785%   $85.2358   $85.24   $85.25   $85.20  
  Purchase #2 $208.85   7.317%   $224.1316   $224.13   $224.15   $224.10  
  Purchase #3 $230.66   6.363%   $245.3369   $245.34   $245.35   $245.30  
  Purchase #4 $160.87   8.329%   $174.2689   $174.27   $174.25   $174.30  
  Purchase #5 $126.44   10.363%   $139.543   $139.54   $139.55   $139.50  
  Purchase #6 $10.27   8.617%   $11.155   $11.16   $11.15   $11.20  
  Purchase #7 $153.85   6.579%   $163.9718   $163.97   $163.95   $164.00  
  7 purchase totals = $970.76       $1,043.6430   $1,043.65   $1,043.65   $1,043.60