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	$131.98	3.861%	$137.0757	$137.08	$137.10	$137.10
Purchase #2	$191.68	4.790%	$200.8615	$200.86	$200.85	$200.90
Purchase #3	$11.54	8.717%	$12.5459	$12.55	$12.55	$12.50
Purchase #4	$74.47	13.387%	$84.4393	$84.44	$84.45	$84.40
Purchase #5	$29.45	11.824%	$32.9322	$32.93	$32.95	$32.90
Purchase #6	$99.98	8.154%	$108.1324	$108.13	$108.15	$108.10
Purchase #7	$63.38	3.316%	$65.4817	$65.48	$65.50	$65.50
7 purchase totals =	$602.48		$641.4687	$641.47	$641.55	$641.40