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	$192.54	12.804%	$217.1928	$217.19	$217.20	$217.20
Purchase #2	$75.51	4.322%	$78.7735	$78.77	$78.75	$78.80
Purchase #3	$238.71	10.698%	$264.2472	$264.25	$264.25	$264.20
Purchase #4	$102.81	13.216%	$116.3974	$116.40	$116.40	$116.40
Purchase #5	$196.50	7.321%	$210.8858	$210.89	$210.90	$210.90
Purchase #6	$183.31	6.586%	$195.3828	$195.38	$195.40	$195.40
Purchase #7	$83.95	4.234%	$87.5044	$87.50	$87.50	$87.50
7 purchase totals =	$1,073.33		$1,170.3839	$1,170.38	$1,170.40	$1,170.40