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	$123.98	12.318%	$139.2519	$139.25	$139.25	$139.30
Purchase #2	$147.44	11.743%	$164.7539	$164.75	$164.75	$164.80
Purchase #3	$10.94	12.191%	$12.2737	$12.27	$12.25	$12.30
Purchase #4	$85.38	13.510%	$96.9148	$96.91	$96.90	$96.90
Purchase #5	$48.43	6.462%	$51.5595	$51.56	$51.55	$51.60
Purchase #6	$204.63	10.795%	$226.7198	$226.72	$226.70	$226.70
Purchase #7	$36.62	12.220%	$41.095	$41.10	$41.10	$41.10
7 purchase totals =	$657.42		$732.5686	$732.56	$732.50	$732.70