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 $126.91   11.684%   $141.7382   $141.74   $141.75   $141.70  
  Purchase #2 $245.43   6.860%   $262.2665   $262.27   $262.25   $262.30  
  Purchase #3 $66.34   5.238%   $69.8149   $69.81   $69.80   $69.80  
  Purchase #4 $205.68   12.602%   $231.5998   $231.60   $231.60   $231.60  
  Purchase #5 $184.49   7.530%   $198.3821   $198.38   $198.40   $198.40  
  Purchase #6 $109.70   6.629%   $116.972   $116.97   $116.95   $117.00  
  Purchase #7 $29.79   13.792%   $33.8986   $33.90   $33.90   $33.90  
  7 purchase totals = $968.34       $1,054.6721   $1,054.67   $1,054.65   $1,054.70