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	$6.88	7.466%	$7.3937	$7.39	$7.40	$7.40
Purchase #2	$100.82	8.282%	$109.1699	$109.17	$109.15	$109.20
Purchase #3	$200.83	7.499%	$215.8902	$215.89	$215.90	$215.90
Purchase #4	$74.94	11.739%	$83.7372	$83.74	$83.75	$83.70
Purchase #5	$27.36	4.598%	$28.618	$28.62	$28.60	$28.60
Purchase #6	$128.56	4.832%	$134.772	$134.77	$134.75	$134.80
Purchase #7	$152.26	9.502%	$166.7277	$166.73	$166.75	$166.70
7 purchase totals =	$691.65		$746.3087	$746.31	$746.30	$746.30