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 $218.39   8.230%   $236.3635   $236.36   $236.35   $236.40  
  Purchase #2 $128.76   5.330%   $135.6229   $135.62   $135.60   $135.60  
  Purchase #3 $87.27   12.529%   $98.2041   $98.20   $98.20   $98.20  
  Purchase #4 $185.32   4.332%   $193.3481   $193.35   $193.35   $193.30  
  Purchase #5 $160.80   8.227%   $174.029   $174.03   $174.05   $174.00  
  Purchase #6 $144.65   8.607%   $157.1   $157.10   $157.10   $157.10  
  Purchase #7 $124.29   11.487%   $138.5672   $138.57   $138.55   $138.60  
  7 purchase totals = $1,049.48       $1,133.2348   $1,133.23   $1,133.20   $1,133.20