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 $181.84   10.557%   $201.0368   $201.04   $201.05   $201.00  
  Purchase #2 $59.78   6.432%   $63.625   $63.63   $63.65   $63.60  
  Purchase #3 $23.86   9.331%   $26.0864   $26.09   $26.10   $26.10  
  Purchase #4 $14.61   11.326%   $16.2647   $16.26   $16.25   $16.30  
  Purchase #5 $59.91   7.613%   $64.4709   $64.47   $64.45   $64.50  
  Purchase #6 $218.92   6.167%   $232.4208   $232.42   $232.40   $232.40  
  Purchase #7 $56.93   9.537%   $62.3594   $62.36   $62.35   $62.40  
  7 purchase totals = $615.85       $666.2640   $666.27   $666.25   $666.30