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	$17.91	4.764%	$18.7632	$18.76	$18.75	$18.80
Purchase #2	$177.47	4.180%	$184.8882	$184.89	$184.90	$184.90
Purchase #3	$26.82	3.655%	$27.8003	$27.80	$27.80	$27.80
Purchase #4	$148.46	5.360%	$156.4175	$156.42	$156.40	$156.40
Purchase #5	$224.46	5.809%	$237.4989	$237.50	$237.50	$237.50
Purchase #6	$123.41	4.833%	$129.3744	$129.37	$129.35	$129.40
Purchase #7	$175.93	6.614%	$187.566	$187.57	$187.55	$187.60
7 purchase totals =	$894.46		$942.3085	$942.31	$942.25	$942.40