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 $195.26   4.659%   $204.3572   $204.36   $204.35   $204.40  
  Purchase #2 $76.78   3.341%   $79.3452   $79.35   $79.35   $79.30  
  Purchase #3 $52.27   10.551%   $57.785   $57.79   $57.80   $57.80  
  Purchase #4 $170.30   11.230%   $189.4247   $189.42   $189.40   $189.40  
  Purchase #5 $20.35   8.250%   $22.0289   $22.03   $22.05   $22.00  
  Purchase #6 $59.50   9.200%   $64.974   $64.97   $64.95   $65.00  
  Purchase #7 $196.81   6.417%   $209.4393   $209.44   $209.45   $209.40  
  7 purchase totals = $771.27       $827.3543   $827.36   $827.35   $827.30