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	$225.37	5.684%	$238.18	$238.18	$238.20	$238.20
Purchase #2	$122.53	13.759%	$139.3889	$139.39	$139.40	$139.40
Purchase #3	$219.72	5.503%	$231.8112	$231.81	$231.80	$231.80
Purchase #4	$180.83	6.264%	$192.1572	$192.16	$192.15	$192.20
Purchase #5	$36.48	6.173%	$38.7319	$38.73	$38.75	$38.70
Purchase #6	$192.71	3.435%	$199.3296	$199.33	$199.35	$199.30
Purchase #7	$173.98	12.820%	$196.2842	$196.28	$196.30	$196.30
7 purchase totals =	$1,151.62		$1,235.8830	$1,235.88	$1,235.95	$1,235.90