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	$91.48	5.285%	$96.3147	$96.31	$96.30	$96.30
Purchase #2	$54.68	9.528%	$59.8899	$59.89	$59.90	$59.90
Purchase #3	$96.89	4.295%	$101.0514	$101.05	$101.05	$101.10
Purchase #4	$209.76	6.706%	$223.8265	$223.83	$223.85	$223.80
Purchase #5	$99.53	9.546%	$109.0311	$109.03	$109.05	$109.00
Purchase #6	$103.38	4.427%	$107.9566	$107.96	$107.95	$108.00
Purchase #7	$160.32	7.394%	$172.1741	$172.17	$172.15	$172.20
7 purchase totals =	$816.04		$870.2443	$870.24	$870.25	$870.30