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 $60.26   9.502%   $65.9859   $65.99   $66.00   $66.00  
  Purchase #2 $202.81   6.757%   $216.5139   $216.51   $216.50   $216.50  
  Purchase #3 $19.58   6.154%   $20.785   $20.79   $20.80   $20.80  
  Purchase #4 $230.67   4.680%   $241.4654   $241.47   $241.45   $241.50  
  Purchase #5 $195.54   8.482%   $212.1257   $212.13   $212.15   $212.10  
  Purchase #6 $36.40   4.407%   $38.0041   $38.00   $38.00   $38.00  
  Purchase #7 $144.48   6.285%   $153.5606   $153.56   $153.55   $153.60  
  7 purchase totals = $889.74       $948.4406   $948.45   $948.45   $948.50