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 $114.96   4.440%   $120.0642   $120.06   $120.05   $120.10  
  Purchase #2 $86.52   8.198%   $93.6129   $93.61   $93.60   $93.60  
  Purchase #3 $75.54   11.289%   $84.0677   $84.07   $84.05   $84.10  
  Purchase #4 $69.85   5.193%   $73.4773   $73.48   $73.50   $73.50  
  Purchase #5 $181.51   6.780%   $193.8164   $193.82   $193.80   $193.80  
  Purchase #6 $60.85   10.555%   $67.2727   $67.27   $67.25   $67.30  
  Purchase #7 $119.41   3.612%   $123.7231   $123.72   $123.70   $123.70  
  7 purchase totals = $708.64       $756.0343   $756.03   $755.95   $756.10