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	$52.45	5.153%	$55.1527	$55.15	$55.15	$55.20
Purchase #2	$186.73	9.474%	$204.4208	$204.42	$204.40	$204.40
Purchase #3	$109.77	9.339%	$120.0214	$120.02	$120.00	$120.00
Purchase #4	$95.97	10.306%	$105.8607	$105.86	$105.85	$105.90
Purchase #5	$196.81	9.628%	$215.7589	$215.76	$215.75	$215.80
Purchase #6	$88.62	11.585%	$98.8866	$98.89	$98.90	$98.90
Purchase #7	$100.98	13.170%	$114.2791	$114.28	$114.30	$114.30
7 purchase totals =	$831.33		$914.3802	$914.38	$914.35	$914.50