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 $89.75   6.618%   $95.6897   $95.69   $95.70   $95.70  
  Purchase #2 $20.49   10.221%   $22.5843   $22.58   $22.60   $22.60  
  Purchase #3 $15.60   9.118%   $17.0224   $17.02   $17.00   $17.00  
  Purchase #4 $32.95   10.116%   $36.2832   $36.28   $36.30   $36.30  
  Purchase #5 $16.34   12.395%   $18.3653   $18.37   $18.35   $18.40  
  Purchase #6 $73.26   4.852%   $76.8146   $76.81   $76.80   $76.80  
  Purchase #7 $53.67   9.577%   $58.81   $58.81   $58.80   $58.80  
  7 purchase totals = $302.06       $325.5695   $325.56   $325.55   $325.60