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 $181.75   13.472%   $206.2354   $206.24   $206.25   $206.20  
  Purchase #2 $146.87   11.135%   $163.224   $163.22   $163.20   $163.20  
  Purchase #3 $141.69   11.447%   $157.9093   $157.91   $157.90   $157.90  
  Purchase #4 $118.98   7.525%   $127.9332   $127.93   $127.95   $127.90  
  Purchase #5 $175.46   12.373%   $197.1697   $197.17   $197.15   $197.20  
  Purchase #6 $239.85   6.470%   $255.3683   $255.37   $255.35   $255.40  
  Purchase #7 $151.74   5.719%   $160.418   $160.42   $160.40   $160.40  
  7 purchase totals = $1,156.34       $1,268.2579   $1,268.26   $1,268.20   $1,268.20