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	$173.59	3.239%	$179.2126	$179.21	$179.20	$179.20
Purchase #2	$61.70	13.353%	$69.9388	$69.94	$69.95	$69.90
Purchase #3	$81.83	11.386%	$91.1472	$91.15	$91.15	$91.10
Purchase #4	$99.56	13.434%	$112.9349	$112.93	$112.95	$112.90
Purchase #5	$131.33	13.765%	$149.4076	$149.41	$149.40	$149.40
Purchase #6	$189.52	11.428%	$211.1783	$211.18	$211.20	$211.20
Purchase #7	$73.80	6.270%	$78.4273	$78.43	$78.45	$78.40
7 purchase totals =	$811.33		$892.2467	$892.25	$892.30	$892.10