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 $142.88   13.266%   $161.8345   $161.83   $161.85   $161.80  
  Purchase #2 $224.97   9.194%   $245.6537   $245.65   $245.65   $245.70  
  Purchase #3 $84.76   5.357%   $89.3006   $89.30   $89.30   $89.30  
  Purchase #4 $79.93   12.479%   $89.9045   $89.90   $89.90   $89.90  
  Purchase #5 $180.31   9.513%   $197.4629   $197.46   $197.45   $197.50  
  Purchase #6 $26.88   11.271%   $29.9096   $29.91   $29.90   $29.90  
  Purchase #7 $120.25   13.508%   $136.4934   $136.49   $136.50   $136.50  
  7 purchase totals = $859.98       $950.5592   $950.54   $950.55   $950.60