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 $241.59   4.508%   $252.4809   $252.48   $252.50   $252.50  
  Purchase #2 $176.90   8.846%   $192.5486   $192.55   $192.55   $192.50  
  Purchase #3 $50.98   13.702%   $57.9653   $57.97   $57.95   $58.00  
  Purchase #4 $35.62   6.749%   $38.024   $38.02   $38.00   $38.00  
  Purchase #5 $155.39   3.332%   $160.5676   $160.57   $160.55   $160.60  
  Purchase #6 $97.48   13.845%   $110.9761   $110.98   $111.00   $111.00  
  Purchase #7 $211.86   8.853%   $230.616   $230.62   $230.60   $230.60  
  7 purchase totals = $969.82       $1,043.1785   $1,043.19   $1,043.15   $1,043.20