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 $217.52   7.723%   $234.3191   $234.32   $234.30   $234.30  
  Purchase #2 $172.30   12.270%   $193.4412   $193.44   $193.45   $193.40  
  Purchase #3 $119.56   6.125%   $126.8831   $126.88   $126.90   $126.90  
  Purchase #4 $191.68   5.124%   $201.5017   $201.50   $201.50   $201.50  
  Purchase #5 $79.70   3.633%   $82.5955   $82.60   $82.60   $82.60  
  Purchase #6 $178.65   10.176%   $196.8294   $196.83   $196.85   $196.80  
  Purchase #7 $214.89   4.215%   $223.9476   $223.95   $223.95   $223.90  
  7 purchase totals = $1,174.30       $1,259.5176   $1,259.52   $1,259.55   $1,259.40