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 $237.32   7.870%   $255.9971   $256.00   $256.00   $256.00  
  Purchase #2 $229.74   13.526%   $260.8146   $260.81   $260.80   $260.80  
  Purchase #3 $191.26   12.284%   $214.7544   $214.75   $214.75   $214.80  
  Purchase #4 $56.86   3.779%   $59.0087   $59.01   $59.00   $59.00  
  Purchase #5 $49.27   7.451%   $52.9411   $52.94   $52.95   $52.90  
  Purchase #6 $177.37   11.740%   $198.1932   $198.19   $198.20   $198.20  
  Purchase #7 $23.57   11.523%   $26.286   $26.29   $26.30   $26.30  
  7 purchase totals = $965.39       $1,067.9951   $1,067.99   $1,068.00   $1,068.00