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	$91.27	10.322%	$100.6909	$100.69	$100.70	$100.70
Purchase #2	$42.33	8.430%	$45.8984	$45.90	$45.90	$45.90
Purchase #3	$84.65	6.136%	$89.8441	$89.84	$89.85	$89.80
Purchase #4	$42.87	8.404%	$46.4728	$46.47	$46.45	$46.50
Purchase #5	$8.85	10.336%	$9.7647	$9.76	$9.75	$9.80
Purchase #6	$209.70	6.259%	$222.8251	$222.83	$222.85	$222.80
Purchase #7	$43.98	8.229%	$47.5991	$47.60	$47.60	$47.60
7 purchase totals =	$523.65		$563.0951	$563.09	$563.10	$563.10