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	$120.74	6.756%	$128.8972	$128.90	$128.90	$128.90
Purchase #2	$79.35	13.231%	$89.8488	$89.85	$89.85	$89.80
Purchase #3	$53.44	3.121%	$55.1079	$55.11	$55.10	$55.10
Purchase #4	$196.55	11.370%	$218.8977	$218.90	$218.90	$218.90
Purchase #5	$144.25	3.272%	$148.9699	$148.97	$148.95	$149.00
Purchase #6	$235.77	6.639%	$251.4228	$251.42	$251.40	$251.40
Purchase #7	$105.92	11.203%	$117.7862	$117.79	$117.80	$117.80
7 purchase totals =	$936.02		$1,010.9305	$1,010.94	$1,010.90	$1,010.90