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 $156.43   6.236%   $166.185   $166.19   $166.20   $166.20  
  Purchase #2 $72.94   4.196%   $76.0006   $76.00   $76.00   $76.00  
  Purchase #3 $176.90   7.672%   $190.4718   $190.47   $190.45   $190.50  
  Purchase #4 $230.37   3.300%   $237.9722   $237.97   $237.95   $238.00  
  Purchase #5 $179.68   7.185%   $192.59   $192.59   $192.60   $192.60  
  Purchase #6 $36.51   6.250%   $38.7919   $38.79   $38.80   $38.80  
  Purchase #7 $139.88   5.521%   $147.6028   $147.60   $147.60   $147.60  
  7 purchase totals = $992.71       $1,049.6143   $1,049.61   $1,049.60   $1,049.70