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	$37.86	10.642%	$41.8891	$41.89	$41.90	$41.90
Purchase #2	$48.38	11.858%	$54.1169	$54.12	$54.10	$54.10
Purchase #3	$31.94	12.236%	$35.8482	$35.85	$35.85	$35.80
Purchase #4	$85.93	4.461%	$89.7633	$89.76	$89.75	$89.80
Purchase #5	$80.25	10.753%	$88.8793	$88.88	$88.90	$88.90
Purchase #6	$79.72	11.655%	$89.0114	$89.01	$89.00	$89.00
Purchase #7	$80.78	11.636%	$90.1796	$90.18	$90.20	$90.20
7 purchase totals =	$444.86		$489.6878	$489.69	$489.70	$489.70