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	$140.61	11.263%	$156.4469	$156.45	$156.45	$156.40
Purchase #2	$65.52	7.617%	$70.5107	$70.51	$70.50	$70.50
Purchase #3	$94.37	4.573%	$98.6855	$98.69	$98.70	$98.70
Purchase #4	$90.58	6.568%	$96.5293	$96.53	$96.55	$96.50
Purchase #5	$48.81	10.404%	$53.8882	$53.89	$53.90	$53.90
Purchase #6	$225.66	5.127%	$237.2296	$237.23	$237.25	$237.20
Purchase #7	$100.95	12.772%	$113.8433	$113.84	$113.85	$113.80
7 purchase totals =	$766.50		$827.1335	$827.14	$827.20	$827.00