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 $180.41   9.338%   $197.2567   $197.26   $197.25   $197.30  
  Purchase #2 $156.77   12.479%   $176.3333   $176.33   $176.35   $176.30  
  Purchase #3 $122.54   7.558%   $131.8016   $131.80   $131.80   $131.80  
  Purchase #4 $52.33   11.300%   $58.2433   $58.24   $58.25   $58.20  
  Purchase #5 $182.99   3.444%   $189.2922   $189.29   $189.30   $189.30  
  Purchase #6 $137.76   5.470%   $145.2955   $145.30   $145.30   $145.30  
  Purchase #7 $244.65   6.728%   $261.1101   $261.11   $261.10   $261.10  
  7 purchase totals = $1,077.45       $1,159.3327   $1,159.33   $1,159.35   $1,159.30