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	$200.70	8.826%	$218.4138	$218.41	$218.40	$218.40
Purchase #2	$47.80	9.360%	$52.2741	$52.27	$52.25	$52.30
Purchase #3	$66.64	6.782%	$71.1595	$71.16	$71.15	$71.20
Purchase #4	$67.43	11.700%	$75.3193	$75.32	$75.30	$75.30
Purchase #5	$131.73	5.633%	$139.1504	$139.15	$139.15	$139.20
Purchase #6	$92.65	12.138%	$103.8959	$103.90	$103.90	$103.90
Purchase #7	$223.76	8.543%	$242.8758	$242.88	$242.90	$242.90
7 purchase totals =	$830.71		$903.0888	$903.09	$903.05	$903.20