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	$17.36	11.872%	$19.421	$19.42	$19.40	$19.40
Purchase #2	$211.67	12.666%	$238.4801	$238.48	$238.50	$238.50
Purchase #3	$78.98	4.637%	$82.6423	$82.64	$82.65	$82.60
Purchase #4	$72.48	12.396%	$81.4646	$81.46	$81.45	$81.50
Purchase #5	$59.25	8.500%	$64.2863	$64.29	$64.30	$64.30
Purchase #6	$118.71	11.571%	$132.4459	$132.45	$132.45	$132.40
Purchase #7	$136.96	13.837%	$155.9112	$155.91	$155.90	$155.90
7 purchase totals =	$695.41		$774.6514	$774.65	$774.65	$774.60