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 $95.68   10.809%   $106.0221   $106.02   $106.00   $106.00  
  Purchase #2 $143.29   13.388%   $162.4737   $162.47   $162.45   $162.50  
  Purchase #3 $117.86   4.731%   $123.436   $123.44   $123.45   $123.40  
  Purchase #4 $239.54   6.484%   $255.0718   $255.07   $255.05   $255.10  
  Purchase #5 $171.76   3.489%   $177.7527   $177.75   $177.75   $177.80  
  Purchase #6 $246.63   6.361%   $262.3181   $262.32   $262.30   $262.30  
  Purchase #7 $146.76   10.675%   $162.4266   $162.43   $162.45   $162.40  
  7 purchase totals = $1,161.52       $1,249.5010   $1,249.50   $1,249.45   $1,249.50