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 $61.54   7.703%   $66.2804   $66.28   $66.30   $66.30  
  Purchase #2 $83.96   11.427%   $93.5541   $93.55   $93.55   $93.60  
  Purchase #3 $82.44   9.317%   $90.1209   $90.12   $90.10   $90.10  
  Purchase #4 $235.87   5.232%   $248.2107   $248.21   $248.20   $248.20  
  Purchase #5 $67.79   6.576%   $72.2479   $72.25   $72.25   $72.20  
  Purchase #6 $61.32   12.348%   $68.8918   $68.89   $68.90   $68.90  
  Purchase #7 $119.29   9.571%   $130.7072   $130.71   $130.70   $130.70  
  7 purchase totals = $712.21       $770.0130   $770.01   $770.00   $770.00