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	$135.91	3.421%	$140.5595	$140.56	$140.55	$140.60
Purchase #2	$173.92	6.244%	$184.7796	$184.78	$184.80	$184.80
Purchase #3	$173.59	3.393%	$179.4799	$179.48	$179.50	$179.50
Purchase #4	$48.38	6.809%	$51.6742	$51.67	$51.65	$51.70
Purchase #5	$65.72	13.860%	$74.8288	$74.83	$74.85	$74.80
Purchase #6	$89.75	8.419%	$97.3061	$97.31	$97.30	$97.30
Purchase #7	$127.85	11.736%	$142.8545	$142.85	$142.85	$142.90
7 purchase totals =	$815.12		$871.4826	$871.48	$871.50	$871.60