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 $242.51   8.589%   $263.3392   $263.34   $263.35   $263.30  
  Purchase #2 $213.59   8.870%   $232.5354   $232.54   $232.55   $232.50  
  Purchase #3 $182.44   9.487%   $199.7481   $199.75   $199.75   $199.70  
  Purchase #4 $249.81   13.284%   $282.9948   $282.99   $283.00   $283.00  
  Purchase #5 $196.54   10.816%   $217.7978   $217.80   $217.80   $217.80  
  Purchase #6 $250.89   9.243%   $274.0798   $274.08   $274.10   $274.10  
  Purchase #7 $46.81   13.586%   $53.1696   $53.17   $53.15   $53.20  
  7 purchase totals = $1,382.59       $1,523.6647   $1,523.67   $1,523.70   $1,523.60