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 $53.62   7.707%   $57.7525   $57.75   $57.75   $57.80  
  Purchase #2 $183.67   13.710%   $208.8512   $208.85   $208.85   $208.90  
  Purchase #3 $70.79   5.263%   $74.5157   $74.52   $74.50   $74.50  
  Purchase #4 $97.79   8.332%   $105.9379   $105.94   $105.95   $105.90  
  Purchase #5 $160.71   4.454%   $167.868   $167.87   $167.85   $167.90  
  Purchase #6 $90.86   12.448%   $102.1703   $102.17   $102.15   $102.20  
  Purchase #7 $239.91   11.177%   $266.7247   $266.72   $266.70   $266.70  
  7 purchase totals = $897.35       $983.8203   $983.82   $983.75   $983.90