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	$34.33	7.147%	$36.7836	$36.78	$36.80	$36.80
Purchase #2	$58.92	10.742%	$65.2492	$65.25	$65.25	$65.20
Purchase #3	$246.98	7.114%	$264.5502	$264.55	$264.55	$264.60
Purchase #4	$114.27	11.248%	$127.1231	$127.12	$127.10	$127.10
Purchase #5	$178.32	7.389%	$191.4961	$191.50	$191.50	$191.50
Purchase #6	$232.82	4.495%	$243.2853	$243.29	$243.30	$243.30
Purchase #7	$174.67	9.276%	$190.8724	$190.87	$190.85	$190.90
7 purchase totals =	$1,040.31		$1,119.3599	$1,119.36	$1,119.35	$1,119.40