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	$32.54	12.607%	$36.6423	$36.64	$36.65	$36.60
Purchase #2	$224.67	4.118%	$233.9219	$233.92	$233.90	$233.90
Purchase #3	$94.27	9.794%	$103.5028	$103.50	$103.50	$103.50
Purchase #4	$208.93	6.737%	$223.0056	$223.01	$223.00	$223.00
Purchase #5	$216.68	12.338%	$243.414	$243.41	$243.40	$243.40
Purchase #6	$6.98	12.378%	$7.844	$7.84	$7.85	$7.80
Purchase #7	$109.87	12.340%	$123.428	$123.43	$123.45	$123.40
7 purchase totals =	$893.94		$971.7586	$971.75	$971.75	$971.60