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 $146.70   12.442%   $164.9524   $164.95   $164.95   $165.00  
  Purchase #2 $235.30   5.810%   $248.9709   $248.97   $248.95   $249.00  
  Purchase #3 $75.44   13.817%   $85.8635   $85.86   $85.85   $85.90  
  Purchase #4 $145.52   3.590%   $150.7442   $150.74   $150.75   $150.70  
  Purchase #5 $114.36   9.833%   $125.605   $125.61   $125.60   $125.60  
  Purchase #6 $153.33   13.407%   $173.887   $173.89   $173.90   $173.90  
  Purchase #7 $72.37   6.264%   $76.9033   $76.90   $76.90   $76.90  
  7 purchase totals = $943.02       $1,026.9263   $1,026.92   $1,026.90   $1,027.00