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	$132.97	6.334%	$141.3923	$141.39	$141.40	$141.40
Purchase #2	$54.78	13.830%	$62.3561	$62.36	$62.35	$62.40
Purchase #3	$91.77	3.338%	$94.8333	$94.83	$94.85	$94.80
Purchase #4	$145.40	3.584%	$150.6111	$150.61	$150.60	$150.60
Purchase #5	$40.26	12.647%	$45.3517	$45.35	$45.35	$45.40
Purchase #6	$243.83	8.675%	$264.9823	$264.98	$265.00	$265.00
Purchase #7	$132.77	12.405%	$149.2401	$149.24	$149.25	$149.20
7 purchase totals =	$841.78		$908.7669	$908.76	$908.80	$908.80