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 $168.83   13.302%   $191.2878   $191.29   $191.30   $191.30  
  Purchase #2 $32.26   7.367%   $34.6366   $34.64   $34.65   $34.60  
  Purchase #3 $123.41   8.263%   $133.6074   $133.61   $133.60   $133.60  
  Purchase #4 $162.67   5.368%   $171.4021   $171.40   $171.40   $171.40  
  Purchase #5 $189.64   13.455%   $215.1561   $215.16   $215.15   $215.20  
  Purchase #6 $179.88   4.768%   $188.4567   $188.46   $188.45   $188.50  
  Purchase #7 $176.91   3.310%   $182.7657   $182.77   $182.75   $182.80  
  7 purchase totals = $1,033.60       $1,117.3124   $1,117.33   $1,117.30   $1,117.40