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	$56.31	8.154%	$60.9015	$60.90	$60.90	$60.90
Purchase #2	$190.28	13.682%	$216.3141	$216.31	$216.30	$216.30
Purchase #3	$78.96	13.545%	$89.6551	$89.66	$89.65	$89.70
Purchase #4	$79.76	11.657%	$89.0576	$89.06	$89.05	$89.10
Purchase #5	$130.86	12.230%	$146.8642	$146.86	$146.85	$146.90
Purchase #6	$23.58	6.465%	$25.1044	$25.10	$25.10	$25.10
Purchase #7	$211.74	6.317%	$225.1156	$225.12	$225.10	$225.10
7 purchase totals =	$771.49		$853.0125	$853.01	$852.95	$853.10