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 $53.44   4.503%   $55.8464   $55.85   $55.85   $55.80  
  Purchase #2 $226.85   6.506%   $241.6089   $241.61   $241.60   $241.60  
  Purchase #3 $136.48   6.799%   $145.7593   $145.76   $145.75   $145.80  
  Purchase #4 $175.44   5.608%   $185.2787   $185.28   $185.30   $185.30  
  Purchase #5 $81.91   5.410%   $86.3413   $86.34   $86.35   $86.30  
  Purchase #6 $131.89   6.479%   $140.4352   $140.44   $140.45   $140.40  
  Purchase #7 $187.29   7.670%   $201.6551   $201.66   $201.65   $201.70  
  7 purchase totals = $993.30       $1,056.9249   $1,056.94   $1,056.95   $1,056.90