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	$107.71	11.812%	$120.4327	$120.43	$120.45	$120.40
Purchase #2	$112.79	12.699%	$127.1132	$127.11	$127.10	$127.10
Purchase #3	$208.97	3.129%	$215.5087	$215.51	$215.50	$215.50
Purchase #4	$135.33	5.162%	$142.3157	$142.32	$142.30	$142.30
Purchase #5	$183.71	6.578%	$195.7944	$195.79	$195.80	$195.80
Purchase #6	$9.96	6.745%	$10.6318	$10.63	$10.65	$10.60
Purchase #7	$182.77	4.825%	$191.5887	$191.59	$191.60	$191.60
7 purchase totals =	$941.24		$1,003.3852	$1,003.38	$1,003.40	$1,003.30