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 $146.79   3.426%   $151.819   $151.82   $151.80   $151.80  
  Purchase #2 $249.47   5.371%   $262.869   $262.87   $262.85   $262.90  
  Purchase #3 $159.56   5.445%   $168.248   $168.25   $168.25   $168.20  
  Purchase #4 $231.58   3.533%   $239.7617   $239.76   $239.75   $239.80  
  Purchase #5 $202.49   8.658%   $220.0216   $220.02   $220.00   $220.00  
  Purchase #6 $62.72   7.365%   $67.3393   $67.34   $67.35   $67.30  
  Purchase #7 $88.74   4.444%   $92.6836   $92.68   $92.70   $92.70  
  7 purchase totals = $1,141.35       $1,202.7422   $1,202.74   $1,202.70   $1,202.70