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 $160.98   3.518%   $166.6433   $166.64   $166.65   $166.60  
  Purchase #2 $232.65   12.403%   $261.5056   $261.51   $261.50   $261.50  
  Purchase #3 $99.51   5.678%   $105.1602   $105.16   $105.15   $105.20  
  Purchase #4 $176.87   9.131%   $193.02   $193.02   $193.00   $193.00  
  Purchase #5 $79.70   11.608%   $88.9516   $88.95   $88.95   $89.00  
  Purchase #6 $196.94   5.834%   $208.4295   $208.43   $208.45   $208.40  
  Purchase #7 $218.60   6.359%   $232.5008   $232.50   $232.50   $232.50  
  7 purchase totals = $1,165.25       $1,256.2110   $1,256.21   $1,256.20   $1,256.20