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	$27.64	9.253%	$30.1975	$30.20	$30.20	$30.20
Purchase #2	$189.30	11.648%	$211.3497	$211.35	$211.35	$211.30
Purchase #3	$194.48	11.236%	$216.3318	$216.33	$216.35	$216.30
Purchase #4	$35.61	4.142%	$37.085	$37.09	$37.10	$37.10
Purchase #5	$36.51	5.236%	$38.4217	$38.42	$38.40	$38.40
Purchase #6	$200.78	13.834%	$228.5559	$228.56	$228.55	$228.60
Purchase #7	$221.53	9.512%	$242.6019	$242.60	$242.60	$242.60
7 purchase totals =	$905.85		$1,004.5435	$1,004.55	$1,004.55	$1,004.50