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 $145.92   8.244%   $157.9496   $157.95   $157.95   $157.90  
  Purchase #2 $166.69   6.216%   $177.0515   $177.05   $177.05   $177.10  
  Purchase #3 $164.98   6.769%   $176.1475   $176.15   $176.15   $176.10  
  Purchase #4 $248.90   11.106%   $276.5428   $276.54   $276.55   $276.50  
  Purchase #5 $40.51   6.306%   $43.0646   $43.06   $43.05   $43.10  
  Purchase #6 $27.92   10.180%   $30.7623   $30.76   $30.75   $30.80  
  Purchase #7 $133.70   6.371%   $142.218   $142.22   $142.20   $142.20  
  7 purchase totals = $928.62       $1,003.7363   $1,003.73   $1,003.70   $1,003.70