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 $76.55   9.521%   $83.8383   $83.84   $83.85   $83.80  
  Purchase #2 $98.28   12.684%   $110.7458   $110.75   $110.75   $110.70  
  Purchase #3 $25.58   12.718%   $28.8333   $28.83   $28.85   $28.80  
  Purchase #4 $173.56   6.681%   $185.1555   $185.16   $185.15   $185.20  
  Purchase #5 $19.52   5.746%   $20.6416   $20.64   $20.65   $20.60  
  Purchase #6 $207.37   7.287%   $222.4811   $222.48   $222.50   $222.50  
  Purchase #7 $121.68   5.184%   $127.9879   $127.99   $128.00   $128.00  
  7 purchase totals = $722.54       $779.6835   $779.69   $779.75   $779.60