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	$82.25	8.565%	$89.2947	$89.29	$89.30	$89.30
Purchase #2	$91.47	7.724%	$98.5351	$98.54	$98.55	$98.50
Purchase #3	$45.71	10.449%	$50.4862	$50.49	$50.50	$50.50
Purchase #4	$149.66	11.519%	$166.8993	$166.90	$166.90	$166.90
Purchase #5	$128.76	8.712%	$139.9776	$139.98	$140.00	$140.00
Purchase #6	$168.29	7.494%	$180.9017	$180.90	$180.90	$180.90
Purchase #7	$153.66	10.500%	$169.7943	$169.79	$169.80	$169.80
7 purchase totals =	$819.80		$895.8889	$895.89	$895.95	$895.90