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	$96.49	5.147%	$101.4563	$101.46	$101.45	$101.50
Purchase #2	$55.32	7.240%	$59.3252	$59.33	$59.35	$59.30
Purchase #3	$73.96	9.497%	$80.984	$80.98	$81.00	$81.00
Purchase #4	$52.76	5.168%	$55.4866	$55.49	$55.50	$55.50
Purchase #5	$123.88	12.351%	$139.1804	$139.18	$139.20	$139.20
Purchase #6	$34.25	9.108%	$37.3695	$37.37	$37.35	$37.40
Purchase #7	$58.48	5.575%	$61.7403	$61.74	$61.75	$61.70
7 purchase totals =	$495.14		$535.5423	$535.55	$535.60	$535.60