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 $207.37   8.233%   $224.4428   $224.44   $224.45   $224.40  
  Purchase #2 $204.42   4.659%   $213.9439   $213.94   $213.95   $213.90  
  Purchase #3 $24.51   9.641%   $26.873   $26.87   $26.85   $26.90  
  Purchase #4 $145.54   5.442%   $153.4603   $153.46   $153.45   $153.50  
  Purchase #5 $200.25   13.206%   $226.695   $226.70   $226.70   $226.70  
  Purchase #6 $195.68   3.570%   $202.6658   $202.67   $202.65   $202.70  
  Purchase #7 $24.55   8.262%   $26.5783   $26.58   $26.60   $26.60  
  7 purchase totals = $1,002.32       $1,074.6591   $1,074.66   $1,074.65   $1,074.70