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	$75.51	3.773%	$78.359	$78.36	$78.35	$78.40
Purchase #2	$27.75	12.831%	$31.3106	$31.31	$31.30	$31.30
Purchase #3	$118.88	6.850%	$127.0233	$127.02	$127.00	$127.00
Purchase #4	$110.49	10.711%	$122.3246	$122.32	$122.30	$122.30
Purchase #5	$138.53	5.549%	$146.217	$146.22	$146.20	$146.20
Purchase #6	$107.56	7.791%	$115.94	$115.94	$115.95	$115.90
Purchase #7	$213.91	12.377%	$240.3856	$240.39	$240.40	$240.40
7 purchase totals =	$792.63		$861.5601	$861.56	$861.50	$861.50