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	$78.66	5.383%	$82.8943	$82.89	$82.90	$82.90
Purchase #2	$245.93	9.570%	$269.4655	$269.47	$269.45	$269.50
Purchase #3	$197.33	4.519%	$206.2473	$206.25	$206.25	$206.20
Purchase #4	$69.27	13.242%	$78.4427	$78.44	$78.45	$78.40
Purchase #5	$91.71	5.584%	$96.8311	$96.83	$96.85	$96.80
Purchase #6	$190.92	6.604%	$203.5284	$203.53	$203.55	$203.50
Purchase #7	$141.30	7.153%	$151.4072	$151.41	$151.40	$151.40
7 purchase totals =	$1,015.12		$1,088.8165	$1,088.82	$1,088.85	$1,088.70