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	$39.25	4.723%	$41.1038	$41.10	$41.10	$41.10
Purchase #2	$73.63	6.285%	$78.2576	$78.26	$78.25	$78.30
Purchase #3	$85.74	4.678%	$89.7509	$89.75	$89.75	$89.80
Purchase #4	$207.27	4.582%	$216.7671	$216.77	$216.75	$216.80
Purchase #5	$185.25	5.822%	$196.0353	$196.04	$196.05	$196.00
Purchase #6	$183.66	11.295%	$204.4044	$204.40	$204.40	$204.40
Purchase #7	$72.41	10.256%	$79.8364	$79.84	$79.85	$79.80
7 purchase totals =	$847.21		$906.1555	$906.16	$906.15	$906.20