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 $106.46   11.782%   $119.0031   $119.00   $119.00   $119.00  
  Purchase #2 $248.67   6.458%   $264.7291   $264.73   $264.75   $264.70  
  Purchase #3 $250.96   6.492%   $267.2523   $267.25   $267.25   $267.30  
  Purchase #4 $23.58   3.508%   $24.4072   $24.41   $24.40   $24.40  
  Purchase #5 $239.52   8.237%   $259.2493   $259.25   $259.25   $259.20  
  Purchase #6 $101.77   3.177%   $105.0032   $105.00   $105.00   $105.00  
  Purchase #7 $24.59   7.445%   $26.4207   $26.42   $26.40   $26.40  
  7 purchase totals = $995.55       $1,066.0649   $1,066.06   $1,066.05   $1,066.00