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 $56.31   11.776%   $62.9411   $62.94   $62.95   $62.90  
  Purchase #2 $7.68   3.239%   $7.9288   $7.93   $7.95   $7.90  
  Purchase #3 $7.74   5.495%   $8.1653   $8.17   $8.15   $8.20  
  Purchase #4 $221.79   4.771%   $232.3716   $232.37   $232.35   $232.40  
  Purchase #5 $25.72   13.526%   $29.1989   $29.20   $29.20   $29.20  
  Purchase #6 $160.89   6.683%   $171.6423   $171.64   $171.65   $171.60  
  Purchase #7 $231.77   9.596%   $254.0106   $254.01   $254.00   $254.00  
  7 purchase totals = $711.90       $766.2586   $766.26   $766.25   $766.20