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 $94.98   6.480%   $101.1347   $101.13   $101.15   $101.10  
  Purchase #2 $166.55   12.859%   $187.9667   $187.97   $187.95   $188.00  
  Purchase #3 $211.39   6.267%   $224.6378   $224.64   $224.65   $224.60  
  Purchase #4 $61.59   9.599%   $67.502   $67.50   $67.50   $67.50  
  Purchase #5 $218.52   10.829%   $242.1835   $242.18   $242.20   $242.20  
  Purchase #6 $234.50   11.584%   $261.6645   $261.66   $261.65   $261.70  
  Purchase #7 $81.64   5.694%   $86.2886   $86.29   $86.30   $86.30  
  7 purchase totals = $1,069.17       $1,171.3778   $1,171.37   $1,171.40   $1,171.40