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 $197.42   8.779%   $214.7515   $214.75   $214.75   $214.80  
  Purchase #2 $141.91   5.822%   $150.172   $150.17   $150.15   $150.20  
  Purchase #3 $82.74   7.214%   $88.7089   $88.71   $88.70   $88.70  
  Purchase #4 $230.61   9.102%   $251.6001   $251.60   $251.60   $251.60  
  Purchase #5 $160.53   10.404%   $177.2315   $177.23   $177.25   $177.20  
  Purchase #6 $58.46   8.824%   $63.6185   $63.62   $63.60   $63.60  
  Purchase #7 $73.92   3.699%   $76.6543   $76.65   $76.65   $76.70  
  7 purchase totals = $945.59       $1,022.7368   $1,022.73   $1,022.70   $1,022.80