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 $249.80   9.558%   $273.6759   $273.68   $273.70   $273.70  
  Purchase #2 $205.83   10.145%   $226.7115   $226.71   $226.70   $226.70  
  Purchase #3 $111.91   6.515%   $119.2009   $119.20   $119.20   $119.20  
  Purchase #4 $188.35   6.851%   $201.2539   $201.25   $201.25   $201.30  
  Purchase #5 $57.95   12.573%   $65.2361   $65.24   $65.25   $65.20  
  Purchase #6 $99.44   7.240%   $106.6395   $106.64   $106.65   $106.60  
  Purchase #7 $231.58   8.134%   $250.4167   $250.42   $250.40   $250.40  
  7 purchase totals = $1,144.86       $1,243.1345   $1,243.14   $1,243.15   $1,243.10