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	$198.79	9.792%	$218.2555	$218.26	$218.25	$218.30
Purchase #2	$219.59	11.749%	$245.3896	$245.39	$245.40	$245.40
Purchase #3	$136.50	6.642%	$145.5663	$145.57	$145.55	$145.60
Purchase #4	$56.72	10.154%	$62.4793	$62.48	$62.50	$62.50
Purchase #5	$156.38	3.681%	$162.1363	$162.14	$162.15	$162.10
Purchase #6	$40.82	13.732%	$46.4254	$46.43	$46.45	$46.40
Purchase #7	$115.56	3.190%	$119.2464	$119.25	$119.25	$119.20
7 purchase totals =	$924.36		$999.4988	$999.52	$999.55	$999.50