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 $31.65   11.626%   $35.3296   $35.33   $35.35   $35.30  
  Purchase #2 $110.85   4.105%   $115.4004   $115.40   $115.40   $115.40  
  Purchase #3 $35.32   8.703%   $38.3939   $38.39   $38.40   $38.40  
  Purchase #4 $198.79   13.562%   $225.7499   $225.75   $225.75   $225.70  
  Purchase #5 $23.84   4.154%   $24.8303   $24.83   $24.85   $24.80  
  Purchase #6 $146.92   3.639%   $152.2664   $152.27   $152.25   $152.30  
  Purchase #7 $8.64   6.354%   $9.189   $9.19   $9.20   $9.20  
  7 purchase totals = $556.01       $601.1595   $601.16   $601.20   $601.10