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 $246.25   12.102%   $276.0512   $276.05   $276.05   $276.10  
  Purchase #2 $112.84   4.502%   $117.9201   $117.92   $117.90   $117.90  
  Purchase #3 $190.59   7.799%   $205.4541   $205.45   $205.45   $205.50  
  Purchase #4 $210.41   12.276%   $236.2399   $236.24   $236.25   $236.20  
  Purchase #5 $136.40   8.629%   $148.17   $148.17   $148.15   $148.20  
  Purchase #6 $199.82   7.373%   $214.5527   $214.55   $214.55   $214.60  
  Purchase #7 $23.52   11.810%   $26.2977   $26.30   $26.30   $26.30  
  7 purchase totals = $1,119.83       $1,224.6857   $1,224.68   $1,224.65   $1,224.80