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 $60.76   12.230%   $68.1909   $68.19   $68.20   $68.20  
  Purchase #2 $229.66   10.538%   $253.8616   $253.86   $253.85   $253.90  
  Purchase #3 $181.60   6.189%   $192.8392   $192.84   $192.85   $192.80  
  Purchase #4 $219.98   6.669%   $234.6505   $234.65   $234.65   $234.70  
  Purchase #5 $125.99   6.397%   $134.0496   $134.05   $134.05   $134.00  
  Purchase #6 $18.87   6.862%   $20.1649   $20.16   $20.15   $20.20  
  Purchase #7 $112.89   8.824%   $122.8514   $122.85   $122.85   $122.90  
  7 purchase totals = $949.75       $1,026.6081   $1,026.60   $1,026.60   $1,026.70