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	$68.47	10.581%	$75.7148	$75.71	$75.70	$75.70
Purchase #2	$113.90	4.764%	$119.3262	$119.33	$119.35	$119.30
Purchase #3	$39.60	10.623%	$43.8067	$43.81	$43.80	$43.80
Purchase #4	$103.26	8.337%	$111.8688	$111.87	$111.85	$111.90
Purchase #5	$36.70	11.832%	$41.0423	$41.04	$41.05	$41.00
Purchase #6	$64.47	11.490%	$71.8776	$71.88	$71.90	$71.90
Purchase #7	$109.54	10.123%	$120.6287	$120.63	$120.65	$120.60
7 purchase totals =	$535.94		$584.2651	$584.27	$584.30	$584.20