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 $74.39   10.273%   $82.0321   $82.03   $82.05   $82.00  
  Purchase #2 $56.45   13.111%   $63.8512   $63.85   $63.85   $63.90  
  Purchase #3 $20.66   3.663%   $21.4168   $21.42   $21.40   $21.40  
  Purchase #4 $214.61   8.527%   $232.9098   $232.91   $232.90   $232.90  
  Purchase #5 $221.88   13.324%   $251.4433   $251.44   $251.45   $251.40  
  Purchase #6 $189.28   12.445%   $212.8359   $212.84   $212.85   $212.80  
  Purchase #7 $81.35   12.401%   $91.4382   $91.44   $91.45   $91.40  
  7 purchase totals = $858.62       $955.9273   $955.93   $955.95   $955.80