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 $157.38   12.455%   $176.9817   $176.98   $177.00   $177.00  
  Purchase #2 $61.66   11.159%   $68.5406   $68.54   $68.55   $68.50  
  Purchase #3 $231.44   13.697%   $263.1403   $263.14   $263.15   $263.10  
  Purchase #4 $248.90   7.713%   $268.0977   $268.10   $268.10   $268.10  
  Purchase #5 $5.97   7.152%   $6.397   $6.40   $6.40   $6.40  
  Purchase #6 $118.87   9.841%   $130.568   $130.57   $130.55   $130.60  
  Purchase #7 $147.69   6.769%   $157.6871   $157.69   $157.70   $157.70  
  7 purchase totals = $971.91       $1,071.4124   $1,071.42   $1,071.45   $1,071.40