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 $151.69   11.213%   $168.699   $168.70   $168.70   $168.70  
  Purchase #2 $66.80   4.167%   $69.5836   $69.58   $69.60   $69.60  
  Purchase #3 $217.99   6.687%   $232.567   $232.57   $232.55   $232.60  
  Purchase #4 $216.46   7.844%   $233.4391   $233.44   $233.45   $233.40  
  Purchase #5 $134.99   10.559%   $149.2436   $149.24   $149.25   $149.20  
  Purchase #6 $191.30   11.586%   $213.464   $213.46   $213.45   $213.50  
  Purchase #7 $115.70   3.697%   $119.9774   $119.98   $120.00   $120.00  
  7 purchase totals = $1,094.93       $1,186.9737   $1,186.97   $1,187.00   $1,187.00