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 $162.58   12.539%   $182.9659   $182.97   $182.95   $183.00  
  Purchase #2 $6.77   13.223%   $7.6652   $7.67   $7.65   $7.70  
  Purchase #3 $206.44   4.137%   $214.9804   $214.98   $215.00   $215.00  
  Purchase #4 $76.57   10.303%   $84.459   $84.46   $84.45   $84.50  
  Purchase #5 $188.93   4.260%   $196.9784   $196.98   $197.00   $197.00  
  Purchase #6 $225.59   13.558%   $256.1755   $256.18   $256.20   $256.20  
  Purchase #7 $107.85   8.113%   $116.5999   $116.60   $116.60   $116.60  
  7 purchase totals = $974.73       $1,059.8243   $1,059.84   $1,059.85   $1,060.00