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 $210.51   13.303%   $238.5141   $238.51   $238.50   $238.50  
  Purchase #2 $93.47   6.103%   $99.1745   $99.17   $99.15   $99.20  
  Purchase #3 $160.91   13.143%   $182.0584   $182.06   $182.05   $182.10  
  Purchase #4 $135.29   12.535%   $152.2486   $152.25   $152.25   $152.20  
  Purchase #5 $170.37   4.241%   $177.5954   $177.60   $177.60   $177.60  
  Purchase #6 $124.82   9.655%   $136.8714   $136.87   $136.85   $136.90  
  Purchase #7 $70.49   8.682%   $76.6099   $76.61   $76.60   $76.60  
  7 purchase totals = $965.86       $1,063.0723   $1,063.07   $1,063.00   $1,063.10