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 $181.96   6.433%   $193.6655   $193.67   $193.65   $193.70  
  Purchase #2 $57.56   10.605%   $63.6642   $63.66   $63.65   $63.70  
  Purchase #3 $196.79   5.230%   $207.0821   $207.08   $207.10   $207.10  
  Purchase #4 $23.26   6.608%   $24.797   $24.80   $24.80   $24.80  
  Purchase #5 $22.61   7.227%   $24.244   $24.24   $24.25   $24.20  
  Purchase #6 $69.38   4.840%   $72.738   $72.74   $72.75   $72.70  
  Purchase #7 $117.85   12.411%   $132.4764   $132.48   $132.50   $132.50  
  7 purchase totals = $669.41       $718.6672   $718.67   $718.70   $718.70