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	$141.32	4.251%	$147.3275	$147.33	$147.35	$147.30
Purchase #2	$133.55	3.568%	$138.3151	$138.32	$138.30	$138.30
Purchase #3	$93.29	6.800%	$99.6337	$99.63	$99.65	$99.60
Purchase #4	$143.46	12.172%	$160.922	$160.92	$160.90	$160.90
Purchase #5	$109.78	3.154%	$113.2425	$113.24	$113.25	$113.20
Purchase #6	$43.90	10.135%	$48.3493	$48.35	$48.35	$48.30
Purchase #7	$89.74	6.852%	$95.889	$95.89	$95.90	$95.90
7 purchase totals =	$755.04		$803.6791	$803.68	$803.70	$803.50