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	$166.33	3.338%	$171.8821	$171.88	$171.90	$171.90
Purchase #2	$146.43	3.680%	$151.8186	$151.82	$151.80	$151.80
Purchase #3	$205.65	9.418%	$225.0181	$225.02	$225.00	$225.00
Purchase #4	$249.49	8.422%	$270.502	$270.50	$270.50	$270.50
Purchase #5	$92.45	8.506%	$100.3138	$100.31	$100.30	$100.30
Purchase #6	$220.34	13.807%	$250.7623	$250.76	$250.75	$250.80
Purchase #7	$237.88	12.487%	$267.5841	$267.58	$267.60	$267.60
7 purchase totals =	$1,318.57		$1,437.8810	$1,437.87	$1,437.85	$1,437.90