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 $208.82   6.152%   $221.6666   $221.67   $221.65   $221.70  
  Purchase #2 $86.44   7.242%   $92.7   $92.70   $92.70   $92.70  
  Purchase #3 $74.41   9.735%   $81.6538   $81.65   $81.65   $81.70  
  Purchase #4 $25.79   4.312%   $26.9021   $26.90   $26.90   $26.90  
  Purchase #5 $189.54   12.137%   $212.5445   $212.54   $212.55   $212.50  
  Purchase #6 $173.83   5.805%   $183.9208   $183.92   $183.90   $183.90  
  Purchase #7 $175.34   11.348%   $195.2376   $195.24   $195.25   $195.20  
  7 purchase totals = $934.17       $1,014.6254   $1,014.62   $1,014.60   $1,014.60