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 $86.33   9.186%   $94.2603   $94.26   $94.25   $94.30  
  Purchase #2 $80.62   10.602%   $89.1673   $89.17   $89.15   $89.20  
  Purchase #3 $116.58   8.805%   $126.8449   $126.84   $126.85   $126.80  
  Purchase #4 $60.28   5.402%   $63.5363   $63.54   $63.55   $63.50  
  Purchase #5 $208.61   4.525%   $218.0496   $218.05   $218.05   $218.00  
  Purchase #6 $115.95   7.119%   $124.2045   $124.20   $124.20   $124.20  
  Purchase #7 $59.49   9.761%   $65.2968   $65.30   $65.30   $65.30  
  7 purchase totals = $727.86       $781.3597   $781.36   $781.35   $781.30