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	$96.44	12.109%	$108.1179	$108.12	$108.10	$108.10
Purchase #2	$26.36	8.623%	$28.633	$28.63	$28.65	$28.60
Purchase #3	$26.27	13.580%	$29.8375	$29.84	$29.85	$29.80
Purchase #4	$79.61	5.443%	$83.9432	$83.94	$83.95	$83.90
Purchase #5	$92.99	6.416%	$98.9562	$98.96	$98.95	$99.00
Purchase #6	$85.59	3.654%	$88.7175	$88.72	$88.70	$88.70
Purchase #7	$64.83	11.121%	$72.0397	$72.04	$72.05	$72.00
7 purchase totals =	$472.09		$510.2450	$510.25	$510.25	$510.10