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	$39.31	11.467%	$43.8177	$43.82	$43.80	$43.80
Purchase #2	$97.89	6.761%	$104.5083	$104.51	$104.50	$104.50
Purchase #3	$110.61	13.424%	$125.4583	$125.46	$125.45	$125.50
Purchase #4	$92.92	5.743%	$98.2564	$98.26	$98.25	$98.30
Purchase #5	$70.91	10.744%	$78.5286	$78.53	$78.55	$78.50
Purchase #6	$58.44	6.512%	$62.2456	$62.25	$62.25	$62.20
Purchase #7	$148.49	6.824%	$158.623	$158.62	$158.60	$158.60
7 purchase totals =	$618.57		$671.4379	$671.45	$671.40	$671.40