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 $188.91   4.644%   $197.683   $197.68   $197.70   $197.70  
  Purchase #2 $131.56   6.166%   $139.672   $139.67   $139.65   $139.70  
  Purchase #3 $142.76   6.413%   $151.9152   $151.92   $151.90   $151.90  
  Purchase #4 $103.26   10.185%   $113.777   $113.78   $113.80   $113.80  
  Purchase #5 $77.44   3.254%   $79.9599   $79.96   $79.95   $80.00  
  Purchase #6 $196.50   11.397%   $218.8951   $218.90   $218.90   $218.90  
  Purchase #7 $82.68   4.475%   $86.3799   $86.38   $86.40   $86.40  
  7 purchase totals = $923.11       $988.2821   $988.29   $988.30   $988.40