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	$106.34	11.488%	$118.5563	$118.56	$118.55	$118.60
Purchase #2	$79.54	3.197%	$82.0829	$82.08	$82.10	$82.10
Purchase #3	$145.25	13.750%	$165.2219	$165.22	$165.20	$165.20
Purchase #4	$185.88	4.309%	$193.8896	$193.89	$193.90	$193.90
Purchase #5	$33.53	10.489%	$37.047	$37.05	$37.05	$37.00
Purchase #6	$48.48	9.595%	$53.1317	$53.13	$53.15	$53.10
Purchase #7	$25.98	7.330%	$27.8843	$27.88	$27.90	$27.90
7 purchase totals =	$625.00		$677.8137	$677.81	$677.85	$677.80