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 $203.53   12.600%   $229.1748   $229.17   $229.15   $229.20  
  Purchase #2 $171.96   6.217%   $182.6508   $182.65   $182.65   $182.70  
  Purchase #3 $84.87   8.350%   $91.9566   $91.96   $91.95   $92.00  
  Purchase #4 $235.46   5.703%   $248.8883   $248.89   $248.90   $248.90  
  Purchase #5 $158.77   8.158%   $171.7225   $171.72   $171.70   $171.70  
  Purchase #6 $58.65   5.305%   $61.7614   $61.76   $61.75   $61.80  
  Purchase #7 $73.98   10.168%   $81.5023   $81.50   $81.50   $81.50  
  7 purchase totals = $987.22       $1,067.6567   $1,067.65   $1,067.60   $1,067.80