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 $82.66   13.303%   $93.6563   $93.66   $93.65   $93.70  
  Purchase #2 $201.95   6.202%   $214.4749   $214.47   $214.45   $214.50  
  Purchase #3 $132.53   9.650%   $145.3191   $145.32   $145.30   $145.30  
  Purchase #4 $246.87   10.517%   $272.8333   $272.83   $272.85   $272.80  
  Purchase #5 $232.55   5.599%   $245.5705   $245.57   $245.55   $245.60  
  Purchase #6 $185.62   13.764%   $211.1687   $211.17   $211.15   $211.20  
  Purchase #7 $100.99   4.279%   $105.3114   $105.31   $105.30   $105.30  
  7 purchase totals = $1,183.17       $1,288.3342   $1,288.33   $1,288.25   $1,288.40