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 $244.41   12.294%   $274.4578   $274.46   $274.45   $274.50  
  Purchase #2 $197.72   8.445%   $214.4175   $214.42   $214.40   $214.40  
  Purchase #3 $204.79   4.676%   $214.366   $214.37   $214.35   $214.40  
  Purchase #4 $216.56   13.542%   $245.8866   $245.89   $245.90   $245.90  
  Purchase #5 $201.82   4.551%   $211.0048   $211.00   $211.00   $211.00  
  Purchase #6 $105.99   12.501%   $119.2398   $119.24   $119.25   $119.20  
  Purchase #7 $187.88   7.301%   $201.5971   $201.60   $201.60   $201.60  
  7 purchase totals = $1,359.17       $1,480.9696   $1,480.98   $1,480.95   $1,481.00