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 $81.43   6.728%   $86.9086   $86.91   $86.90   $86.90  
  Purchase #2 $140.82   8.198%   $152.3644   $152.36   $152.35   $152.40  
  Purchase #3 $176.93   11.861%   $197.9157   $197.92   $197.90   $197.90  
  Purchase #4 $177.49   4.301%   $185.1238   $185.12   $185.10   $185.10  
  Purchase #5 $238.66   6.529%   $254.2421   $254.24   $254.25   $254.20  
  Purchase #6 $195.81   11.429%   $218.1891   $218.19   $218.20   $218.20  
  Purchase #7 $175.29   11.861%   $196.0811   $196.08   $196.10   $196.10  
  7 purchase totals = $1,186.43       $1,290.8248   $1,290.82   $1,290.80   $1,290.80