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	$240.77	4.569%	$251.7708	$251.77	$251.75	$251.80
Purchase #2	$80.57	12.401%	$90.5615	$90.56	$90.55	$90.60
Purchase #3	$96.57	9.518%	$105.7615	$105.76	$105.75	$105.80
Purchase #4	$62.46	3.753%	$64.8041	$64.80	$64.80	$64.80
Purchase #5	$122.89	13.439%	$139.4052	$139.41	$139.40	$139.40
Purchase #6	$112.89	13.377%	$127.9913	$127.99	$128.00	$128.00
Purchase #7	$149.92	8.112%	$162.0815	$162.08	$162.10	$162.10
7 purchase totals =	$866.07		$942.3759	$942.37	$942.35	$942.50