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	$74.38	7.372%	$79.8633	$79.86	$79.85	$79.90
Purchase #2	$38.46	13.818%	$43.7744	$43.77	$43.75	$43.80
Purchase #3	$78.36	8.702%	$85.1789	$85.18	$85.20	$85.20
Purchase #4	$91.94	3.510%	$95.1671	$95.17	$95.15	$95.20
Purchase #5	$172.59	8.429%	$187.1376	$187.14	$187.15	$187.10
Purchase #6	$51.53	3.120%	$53.1377	$53.14	$53.15	$53.10
Purchase #7	$232.38	11.825%	$259.8589	$259.86	$259.85	$259.90
7 purchase totals =	$739.64		$804.1179	$804.12	$804.10	$804.20