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	$96.73	4.190%	$100.783	$100.78	$100.80	$100.80
Purchase #2	$166.41	11.118%	$184.9115	$184.91	$184.90	$184.90
Purchase #3	$232.54	13.870%	$264.7933	$264.79	$264.80	$264.80
Purchase #4	$74.92	4.461%	$78.2622	$78.26	$78.25	$78.30
Purchase #5	$233.77	7.185%	$250.5664	$250.57	$250.55	$250.60
Purchase #6	$127.38	9.144%	$139.0276	$139.03	$139.05	$139.00
Purchase #7	$227.94	12.614%	$256.6924	$256.69	$256.70	$256.70
7 purchase totals =	$1,159.69		$1,275.0364	$1,275.03	$1,275.05	$1,275.10