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 $151.72   3.267%   $156.6767   $156.68   $156.70   $156.70  
  Purchase #2 $213.29   6.226%   $226.5694   $226.57   $226.55   $226.60  
  Purchase #3 $86.63   5.242%   $91.1711   $91.17   $91.15   $91.20  
  Purchase #4 $189.91   12.685%   $214.0001   $214.00   $214.00   $214.00  
  Purchase #5 $9.80   10.438%   $10.8229   $10.82   $10.80   $10.80  
  Purchase #6 $73.99   3.151%   $76.3214   $76.32   $76.30   $76.30  
  Purchase #7 $202.56   4.170%   $211.0068   $211.01   $211.00   $211.00  
  7 purchase totals = $927.90       $986.5684   $986.57   $986.50   $986.60