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 $126.55   4.766%   $132.5814   $132.58   $132.60   $132.60  
  Purchase #2 $84.87   13.771%   $96.5574   $96.56   $96.55   $96.60  
  Purchase #3 $65.64   8.121%   $70.9706   $70.97   $70.95   $71.00  
  Purchase #4 $224.60   9.292%   $245.4698   $245.47   $245.45   $245.50  
  Purchase #5 $22.72   6.831%   $24.272   $24.27   $24.25   $24.30  
  Purchase #6 $95.38   6.727%   $101.7962   $101.80   $101.80   $101.80  
  Purchase #7 $150.53   11.461%   $167.7822   $167.78   $167.80   $167.80  
  7 purchase totals = $770.29       $839.4296   $839.43   $839.40   $839.60