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 $243.93   10.333%   $269.1353   $269.14   $269.15   $269.10  
  Purchase #2 $231.84   5.796%   $245.2774   $245.28   $245.30   $245.30  
  Purchase #3 $71.83   9.414%   $78.5921   $78.59   $78.60   $78.60  
  Purchase #4 $124.57   10.756%   $137.9687   $137.97   $137.95   $138.00  
  Purchase #5 $176.32   11.108%   $195.9056   $195.91   $195.90   $195.90  
  Purchase #6 $156.83   6.697%   $167.3329   $167.33   $167.35   $167.30  
  Purchase #7 $164.87   3.668%   $170.9174   $170.92   $170.90   $170.90  
  7 purchase totals = $1,170.19       $1,265.1294   $1,265.14   $1,265.15   $1,265.10