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	$139.38	13.191%	$157.7656	$157.77	$157.75	$157.80
Purchase #2	$34.44	7.794%	$37.1243	$37.12	$37.10	$37.10
Purchase #3	$218.48	6.740%	$233.2056	$233.21	$233.20	$233.20
Purchase #4	$236.34	5.130%	$248.4642	$248.46	$248.45	$248.50
Purchase #5	$6.75	4.642%	$7.0633	$7.06	$7.05	$7.10
Purchase #6	$65.98	7.180%	$70.7174	$70.72	$70.70	$70.70
Purchase #7	$188.26	4.427%	$196.5943	$196.59	$196.60	$196.60
7 purchase totals =	$889.63		$950.9347	$950.93	$950.85	$951.00