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 $197.31   8.206%   $213.5013   $213.50   $213.50   $213.50  
  Purchase #2 $90.70   5.151%   $95.372   $95.37   $95.35   $95.40  
  Purchase #3 $16.89   5.403%   $17.8026   $17.80   $17.80   $17.80  
  Purchase #4 $203.43   3.597%   $210.7474   $210.75   $210.75   $210.70  
  Purchase #5 $248.69   10.448%   $274.6731   $274.67   $274.65   $274.70  
  Purchase #6 $119.70   7.421%   $128.5829   $128.58   $128.60   $128.60  
  Purchase #7 $186.84   8.316%   $202.3776   $202.38   $202.40   $202.40  
  7 purchase totals = $1,063.56       $1,143.0569   $1,143.05   $1,143.05   $1,143.10