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 $200.86   11.154%   $223.2639   $223.26   $223.25   $223.30  
  Purchase #2 $115.30   6.596%   $122.9052   $122.91   $122.90   $122.90  
  Purchase #3 $116.66   11.417%   $129.9791   $129.98   $130.00   $130.00  
  Purchase #4 $71.58   4.625%   $74.8906   $74.89   $74.90   $74.90  
  Purchase #5 $171.25   6.589%   $182.5337   $182.53   $182.55   $182.50  
  Purchase #6 $60.30   8.798%   $65.6052   $65.61   $65.60   $65.60  
  Purchase #7 $204.62   5.557%   $215.9907   $215.99   $216.00   $216.00  
  7 purchase totals = $940.57       $1,015.1684   $1,015.17   $1,015.20   $1,015.20