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	$54.50	8.424%	$59.0911	$59.09	$59.10	$59.10
Purchase #2	$123.53	10.706%	$136.7551	$136.76	$136.75	$136.80
Purchase #3	$36.27	12.129%	$40.6692	$40.67	$40.65	$40.70
Purchase #4	$23.43	8.361%	$25.389	$25.39	$25.40	$25.40
Purchase #5	$205.37	10.175%	$226.2664	$226.27	$226.25	$226.30
Purchase #6	$151.73	9.740%	$166.5085	$166.51	$166.50	$166.50
Purchase #7	$134.90	10.264%	$148.7461	$148.75	$148.75	$148.70
7 purchase totals =	$729.73		$803.4254	$803.44	$803.40	$803.50