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	$39.53	9.282%	$43.1992	$43.20	$43.20	$43.20
Purchase #2	$42.29	6.433%	$45.0105	$45.01	$45.00	$45.00
Purchase #3	$170.84	5.435%	$180.1252	$180.13	$180.15	$180.10
Purchase #4	$227.78	11.705%	$254.4416	$254.44	$254.45	$254.40
Purchase #5	$99.84	3.641%	$103.4752	$103.48	$103.50	$103.50
Purchase #6	$110.30	3.857%	$114.5543	$114.55	$114.55	$114.60
Purchase #7	$109.88	3.350%	$113.561	$113.56	$113.55	$113.60
7 purchase totals =	$800.46		$854.3670	$854.37	$854.40	$854.40