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 $59.66   12.239%   $66.9618   $66.96   $66.95   $67.00  
  Purchase #2 $118.44   13.677%   $134.639   $134.64   $134.65   $134.60  
  Purchase #3 $240.82   9.581%   $263.893   $263.89   $263.90   $263.90  
  Purchase #4 $210.34   7.721%   $226.5804   $226.58   $226.60   $226.60  
  Purchase #5 $181.60   8.435%   $196.918   $196.92   $196.90   $196.90  
  Purchase #6 $154.98   10.195%   $170.7802   $170.78   $170.80   $170.80  
  Purchase #7 $249.81   8.644%   $271.4036   $271.40   $271.40   $271.40  
  7 purchase totals = $1,215.65       $1,331.1760   $1,331.17   $1,331.20   $1,331.20