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	$101.86	3.285%	$105.2061	$105.21	$105.20	$105.20
Purchase #2	$185.94	9.112%	$202.8829	$202.88	$202.90	$202.90
Purchase #3	$103.59	5.758%	$109.5547	$109.55	$109.55	$109.60
Purchase #4	$141.66	7.608%	$152.4375	$152.44	$152.45	$152.40
Purchase #5	$77.79	13.312%	$88.1454	$88.15	$88.15	$88.10
Purchase #6	$29.67	13.728%	$33.7431	$33.74	$33.75	$33.70
Purchase #7	$233.68	7.116%	$250.3087	$250.31	$250.30	$250.30
7 purchase totals =	$874.19		$942.2784	$942.28	$942.30	$942.20