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 $82.99   12.408%   $93.2874   $93.29   $93.30   $93.30  
  Purchase #2 $86.41   8.419%   $93.6849   $93.68   $93.70   $93.70  
  Purchase #3 $225.46   4.216%   $234.9654   $234.97   $234.95   $235.00  
  Purchase #4 $179.94   11.430%   $200.5071   $200.51   $200.50   $200.50  
  Purchase #5 $205.67   4.106%   $214.1148   $214.11   $214.10   $214.10  
  Purchase #6 $124.86   11.238%   $138.8918   $138.89   $138.90   $138.90  
  Purchase #7 $92.62   11.467%   $103.2407   $103.24   $103.25   $103.20  
  7 purchase totals = $997.95       $1,078.6921   $1,078.69   $1,078.70   $1,078.70