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 $71.61   6.778%   $76.4637   $76.46   $76.45   $76.50  
  Purchase #2 $85.26   13.308%   $96.6064   $96.61   $96.60   $96.60  
  Purchase #3 $56.86   12.113%   $63.7475   $63.75   $63.75   $63.70  
  Purchase #4 $107.35   10.397%   $118.5112   $118.51   $118.50   $118.50  
  Purchase #5 $240.66   10.795%   $266.6392   $266.64   $266.65   $266.60  
  Purchase #6 $13.62   5.245%   $14.3344   $14.33   $14.35   $14.30  
  Purchase #7 $66.75   5.287%   $70.2791   $70.28   $70.30   $70.30  
  7 purchase totals = $642.11       $706.5815   $706.58   $706.60   $706.50