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	$46.92	10.384%	$51.7922	$51.79	$51.80	$51.80
Purchase #2	$57.58	3.194%	$59.4191	$59.42	$59.40	$59.40
Purchase #3	$245.58	10.623%	$271.668	$271.67	$271.65	$271.70
Purchase #4	$96.38	6.151%	$102.3083	$102.31	$102.30	$102.30
Purchase #5	$179.80	7.421%	$193.143	$193.14	$193.15	$193.10
Purchase #6	$91.61	9.682%	$100.4797	$100.48	$100.50	$100.50
Purchase #7	$93.78	6.301%	$99.6891	$99.69	$99.70	$99.70
7 purchase totals =	$811.65		$878.4994	$878.50	$878.50	$878.50