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	$125.88	9.196%	$137.4559	$137.46	$137.45	$137.50
Purchase #2	$169.95	6.363%	$180.7639	$180.76	$180.75	$180.80
Purchase #3	$246.93	13.170%	$279.4507	$279.45	$279.45	$279.50
Purchase #4	$6.93	10.682%	$7.6703	$7.67	$7.65	$7.70
Purchase #5	$186.75	4.607%	$195.3536	$195.35	$195.35	$195.40
Purchase #6	$91.50	11.505%	$102.0271	$102.03	$102.05	$102.00
Purchase #7	$86.80	4.225%	$90.4673	$90.47	$90.45	$90.50
7 purchase totals =	$914.74		$993.1888	$993.19	$993.15	$993.40