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 $60.49   8.683%   $65.7423   $65.74   $65.75   $65.70  
  Purchase #2 $15.82   6.386%   $16.8303   $16.83   $16.85   $16.80  
  Purchase #3 $238.77   12.488%   $268.5876   $268.59   $268.60   $268.60  
  Purchase #4 $84.71   12.214%   $95.0565   $95.06   $95.05   $95.10  
  Purchase #5 $42.27   13.160%   $47.8327   $47.83   $47.85   $47.80  
  Purchase #6 $246.34   8.276%   $266.7271   $266.73   $266.75   $266.70  
  Purchase #7 $231.29   6.331%   $245.933   $245.93   $245.95   $245.90  
  7 purchase totals = $919.69       $1,006.7095   $1,006.71   $1,006.80   $1,006.60