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 $54.70   13.109%   $61.8706   $61.87   $61.85   $61.90  
  Purchase #2 $69.84   13.592%   $79.3327   $79.33   $79.35   $79.30  
  Purchase #3 $242.72   10.119%   $267.2808   $267.28   $267.30   $267.30  
  Purchase #4 $32.99   3.463%   $34.1324   $34.13   $34.15   $34.10  
  Purchase #5 $61.54   8.515%   $66.7801   $66.78   $66.80   $66.80  
  Purchase #6 $21.30   3.597%   $22.0662   $22.07   $22.05   $22.10  
  Purchase #7 $155.84   5.530%   $164.458   $164.46   $164.45   $164.50  
  7 purchase totals = $638.93       $695.9208   $695.92   $695.95   $696.00