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	$57.35	12.505%	$64.5216	$64.52	$64.50	$64.50
Purchase #2	$29.25	11.629%	$32.6515	$32.65	$32.65	$32.70
Purchase #3	$55.58	9.537%	$60.8807	$60.88	$60.90	$60.90
Purchase #4	$211.90	10.503%	$234.1559	$234.16	$234.15	$234.20
Purchase #5	$226.32	10.798%	$250.758	$250.76	$250.75	$250.80
Purchase #6	$67.88	5.277%	$71.462	$71.46	$71.45	$71.50
Purchase #7	$98.85	7.673%	$106.4348	$106.43	$106.45	$106.40
7 purchase totals =	$747.13		$820.8645	$820.86	$820.85	$821.00