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 $232.52   11.405%   $259.0389   $259.04   $259.05   $259.00  
  Purchase #2 $187.76   5.688%   $198.4398   $198.44   $198.45   $198.40  
  Purchase #3 $61.52   3.327%   $63.5668   $63.57   $63.55   $63.60  
  Purchase #4 $191.32   8.366%   $207.3258   $207.33   $207.35   $207.30  
  Purchase #5 $117.62   6.153%   $124.8572   $124.86   $124.85   $124.90  
  Purchase #6 $166.53   9.800%   $182.8499   $182.85   $182.85   $182.80  
  Purchase #7 $61.43   10.255%   $67.7296   $67.73   $67.75   $67.70  
  7 purchase totals = $1,018.70       $1,103.8080   $1,103.82   $1,103.85   $1,103.70