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	$79.54	12.748%	$89.6798	$89.68	$89.70	$89.70
Purchase #2	$223.89	11.826%	$250.3672	$250.37	$250.35	$250.40
Purchase #3	$182.81	11.872%	$204.5132	$204.51	$204.50	$204.50
Purchase #4	$104.46	9.499%	$114.3827	$114.38	$114.40	$114.40
Purchase #5	$138.31	10.367%	$152.6486	$152.65	$152.65	$152.60
Purchase #6	$85.27	6.199%	$90.5559	$90.56	$90.55	$90.60
Purchase #7	$145.61	12.561%	$163.9001	$163.90	$163.90	$163.90
7 purchase totals =	$959.89		$1,066.0475	$1,066.05	$1,066.05	$1,066.10