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	$229.69	3.391%	$237.4788	$237.48	$237.50	$237.50
Purchase #2	$62.93	4.120%	$65.5227	$65.52	$65.50	$65.50
Purchase #3	$139.69	12.300%	$156.8719	$156.87	$156.85	$156.90
Purchase #4	$60.50	3.320%	$62.5086	$62.51	$62.50	$62.50
Purchase #5	$5.56	13.829%	$6.3289	$6.33	$6.35	$6.30
Purchase #6	$185.46	12.340%	$208.3458	$208.35	$208.35	$208.30
Purchase #7	$59.91	13.267%	$67.8583	$67.86	$67.85	$67.90
7 purchase totals =	$743.74		$804.9150	$804.92	$804.90	$804.90