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	$179.86	6.698%	$191.907	$191.91	$191.90	$191.90
Purchase #2	$56.74	10.537%	$62.7187	$62.72	$62.70	$62.70
Purchase #3	$233.86	7.390%	$251.1423	$251.14	$251.15	$251.10
Purchase #4	$163.43	13.510%	$185.5094	$185.51	$185.50	$185.50
Purchase #5	$35.84	8.835%	$39.0065	$39.01	$39.00	$39.00
Purchase #6	$170.62	5.571%	$180.1252	$180.13	$180.15	$180.10
Purchase #7	$20.76	5.259%	$21.8518	$21.85	$21.85	$21.90
7 purchase totals =	$861.11		$932.2609	$932.27	$932.25	$932.20