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 $168.73   4.628%   $176.5388   $176.54   $176.55   $176.50  
  Purchase #2 $69.82   9.538%   $76.4794   $76.48   $76.50   $76.50  
  Purchase #3 $207.27   6.644%   $221.041   $221.04   $221.05   $221.00  
  Purchase #4 $221.43   9.488%   $242.4393   $242.44   $242.45   $242.40  
  Purchase #5 $223.76   10.640%   $247.5681   $247.57   $247.55   $247.60  
  Purchase #6 $143.63   6.119%   $152.4187   $152.42   $152.40   $152.40  
  Purchase #7 $138.72   4.341%   $144.7418   $144.74   $144.75   $144.70  
  7 purchase totals = $1,173.36       $1,261.2271   $1,261.23   $1,261.25   $1,261.10