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 $152.86   13.151%   $172.9626   $172.96   $172.95   $173.00  
  Purchase #2 $244.42   12.329%   $274.5545   $274.55   $274.55   $274.60  
  Purchase #3 $225.88   12.325%   $253.7197   $253.72   $253.70   $253.70  
  Purchase #4 $250.49   5.378%   $263.9614   $263.96   $263.95   $264.00  
  Purchase #5 $35.99   9.558%   $39.4299   $39.43   $39.45   $39.40  
  Purchase #6 $160.90   10.145%   $177.2233   $177.22   $177.20   $177.20  
  Purchase #7 $195.37   3.116%   $201.4577   $201.46   $201.45   $201.50  
  7 purchase totals = $1,265.91       $1,383.3091   $1,383.30   $1,383.25   $1,383.40