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 $64.98   5.490%   $68.5474   $68.55   $68.55   $68.50  
  Purchase #2 $164.85   12.704%   $185.7925   $185.79   $185.80   $185.80  
  Purchase #3 $174.74   7.147%   $187.2287   $187.23   $187.25   $187.20  
  Purchase #4 $46.47   11.637%   $51.8777   $51.88   $51.90   $51.90  
  Purchase #5 $80.57   10.808%   $89.278   $89.28   $89.30   $89.30  
  Purchase #6 $185.26   8.652%   $201.2887   $201.29   $201.30   $201.30  
  Purchase #7 $25.49   8.388%   $27.6281   $27.63   $27.65   $27.60  
  7 purchase totals = $742.36       $811.6411   $811.65   $811.75   $811.60