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 $43.36   6.699%   $46.2647   $46.26   $46.25   $46.30  
  Purchase #2 $236.86   3.293%   $244.6598   $244.66   $244.65   $244.70  
  Purchase #3 $15.67   10.533%   $17.3205   $17.32   $17.30   $17.30  
  Purchase #4 $215.50   7.147%   $230.9018   $230.90   $230.90   $230.90  
  Purchase #5 $77.45   8.671%   $84.1657   $84.17   $84.15   $84.20  
  Purchase #6 $160.47   6.272%   $170.5347   $170.53   $170.55   $170.50  
  Purchase #7 $243.83   13.545%   $276.8568   $276.86   $276.85   $276.90  
  7 purchase totals = $993.14       $1,070.7040   $1,070.70   $1,070.65   $1,070.80