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 $246.84   6.864%   $263.7831   $263.78   $263.80   $263.80  
  Purchase #2 $226.28   11.233%   $251.698   $251.70   $251.70   $251.70  
  Purchase #3 $25.76   8.448%   $27.9362   $27.94   $27.95   $27.90  
  Purchase #4 $51.51   13.504%   $58.4659   $58.47   $58.45   $58.50  
  Purchase #5 $137.99   12.756%   $155.592   $155.59   $155.60   $155.60  
  Purchase #6 $60.62   5.490%   $63.948   $63.95   $63.95   $63.90  
  Purchase #7 $117.29   11.437%   $130.7045   $130.70   $130.70   $130.70  
  7 purchase totals = $866.29       $952.1277   $952.13   $952.15   $952.10