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 $94.32   4.182%   $98.2645   $98.26   $98.25   $98.30  
  Purchase #2 $61.36   10.774%   $67.9709   $67.97   $67.95   $68.00  
  Purchase #3 $238.70   10.371%   $263.4556   $263.46   $263.45   $263.50  
  Purchase #4 $25.97   12.697%   $29.2674   $29.27   $29.25   $29.30  
  Purchase #5 $137.32   12.374%   $154.312   $154.31   $154.30   $154.30  
  Purchase #6 $135.56   13.218%   $153.4783   $153.48   $153.50   $153.50  
  Purchase #7 $18.90   12.382%   $21.2402   $21.24   $21.25   $21.20  
  7 purchase totals = $712.13       $787.9889   $787.99   $787.95   $788.10