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	$180.25	4.753%	$188.8173	$188.82	$188.80	$188.80
Purchase #2	$189.41	11.127%	$210.4857	$210.49	$210.50	$210.50
Purchase #3	$31.59	8.299%	$34.2117	$34.21	$34.20	$34.20
Purchase #4	$127.91	11.793%	$142.9944	$142.99	$143.00	$143.00
Purchase #5	$65.50	8.638%	$71.1579	$71.16	$71.15	$71.20
Purchase #6	$58.72	4.452%	$61.3342	$61.33	$61.35	$61.30
Purchase #7	$84.40	7.107%	$90.3983	$90.40	$90.40	$90.40
7 purchase totals =	$737.78		$799.3995	$799.40	$799.40	$799.40