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	$96.77	6.682%	$103.2362	$103.24	$103.25	$103.20
Purchase #2	$197.46	11.353%	$219.8776	$219.88	$219.90	$219.90
Purchase #3	$35.54	11.181%	$39.5137	$39.51	$39.50	$39.50
Purchase #4	$220.25	9.700%	$241.6143	$241.61	$241.60	$241.60
Purchase #5	$204.93	11.343%	$228.1752	$228.18	$228.20	$228.20
Purchase #6	$202.78	9.561%	$222.1678	$222.17	$222.15	$222.20
Purchase #7	$233.42	11.345%	$259.9015	$259.90	$259.90	$259.90
7 purchase totals =	$1,191.15		$1,314.4863	$1,314.49	$1,314.50	$1,314.50