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	$120.78	6.339%	$128.4362	$128.44	$128.45	$128.40
Purchase #2	$137.33	10.351%	$151.545	$151.55	$151.55	$151.50
Purchase #3	$36.33	10.157%	$40.02	$40.02	$40.00	$40.00
Purchase #4	$57.83	6.333%	$61.4924	$61.49	$61.50	$61.50
Purchase #5	$31.90	12.583%	$35.914	$35.91	$35.90	$35.90
Purchase #6	$21.59	5.417%	$22.7595	$22.76	$22.75	$22.80
Purchase #7	$189.28	5.617%	$199.9119	$199.91	$199.90	$199.90
7 purchase totals =	$595.04		$640.0790	$640.08	$640.05	$640.00