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 $201.89   13.731%   $229.6115   $229.61   $229.60   $229.60  
  Purchase #2 $168.27   11.613%   $187.8112   $187.81   $187.80   $187.80  
  Purchase #3 $29.73   8.483%   $32.252   $32.25   $32.25   $32.30  
  Purchase #4 $160.67   9.417%   $175.8003   $175.80   $175.80   $175.80  
  Purchase #5 $208.65   9.575%   $228.6282   $228.63   $228.65   $228.60  
  Purchase #6 $200.72   8.116%   $217.0104   $217.01   $217.00   $217.00  
  Purchase #7 $51.67   8.751%   $56.1916   $56.19   $56.20   $56.20  
  7 purchase totals = $1,021.60       $1,127.3052   $1,127.30   $1,127.30   $1,127.30