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	$84.97	6.498%	$90.4914	$90.49	$90.50	$90.50
Purchase #2	$134.72	5.606%	$142.2724	$142.27	$142.25	$142.30
Purchase #3	$178.89	9.268%	$195.4695	$195.47	$195.45	$195.50
Purchase #4	$206.96	4.752%	$216.7947	$216.79	$216.80	$216.80
Purchase #5	$105.56	6.736%	$112.6705	$112.67	$112.65	$112.70
Purchase #6	$27.34	11.844%	$30.5781	$30.58	$30.60	$30.60
Purchase #7	$191.84	13.663%	$218.0511	$218.05	$218.05	$218.10
7 purchase totals =	$930.28		$1,006.3277	$1,006.32	$1,006.30	$1,006.50