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 $52.98   5.209%   $55.7397   $55.74   $55.75   $55.70  
  Purchase #2 $192.77   6.662%   $205.6123   $205.61   $205.60   $205.60  
  Purchase #3 $160.77   9.357%   $175.8132   $175.81   $175.80   $175.80  
  Purchase #4 $199.57   6.727%   $212.9951   $213.00   $213.00   $213.00  
  Purchase #5 $83.36   3.528%   $86.3009   $86.30   $86.30   $86.30  
  Purchase #6 $52.37   11.603%   $58.4465   $58.45   $58.45   $58.40  
  Purchase #7 $53.95   4.598%   $56.4306   $56.43   $56.45   $56.40  
  7 purchase totals = $795.77       $851.3383   $851.34   $851.35   $851.20