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 $113.91   3.764%   $118.1976   $118.20   $118.20   $118.20  
  Purchase #2 $173.61   10.374%   $191.6203   $191.62   $191.60   $191.60  
  Purchase #3 $75.28   13.555%   $85.4842   $85.48   $85.50   $85.50  
  Purchase #4 $26.27   5.113%   $27.6132   $27.61   $27.60   $27.60  
  Purchase #5 $79.41   10.713%   $87.9172   $87.92   $87.90   $87.90  
  Purchase #6 $128.38   8.277%   $139.006   $139.01   $139.00   $139.00  
  Purchase #7 $117.81   7.323%   $126.4372   $126.44   $126.45   $126.40  
  7 purchase totals = $714.67       $776.2757   $776.28   $776.25   $776.20