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	$91.46	6.779%	$97.6601	$97.66	$97.65	$97.70
Purchase #2	$134.46	6.109%	$142.6742	$142.67	$142.65	$142.70
Purchase #3	$52.27	7.250%	$56.0596	$56.06	$56.05	$56.10
Purchase #4	$64.70	11.486%	$72.1314	$72.13	$72.15	$72.10
Purchase #5	$141.59	7.528%	$152.2489	$152.25	$152.25	$152.20
Purchase #6	$186.25	9.617%	$204.1617	$204.16	$204.15	$204.20
Purchase #7	$53.56	3.869%	$55.6322	$55.63	$55.65	$55.60
7 purchase totals =	$724.29		$780.5681	$780.56	$780.55	$780.60