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 $92.49   4.705%   $96.8417   $96.84   $96.85   $96.80  
  Purchase #2 $150.87   8.496%   $163.6879   $163.69   $163.70   $163.70  
  Purchase #3 $61.26   8.349%   $66.3746   $66.37   $66.35   $66.40  
  Purchase #4 $201.99   12.820%   $227.8851   $227.89   $227.90   $227.90  
  Purchase #5 $64.76   11.694%   $72.333   $72.33   $72.35   $72.30  
  Purchase #6 $67.46   13.721%   $76.7162   $76.72   $76.70   $76.70  
  Purchase #7 $15.96   13.430%   $18.1034   $18.10   $18.10   $18.10  
  7 purchase totals = $654.79       $721.9419   $721.94   $721.95   $721.90