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	$61.88	9.383%	$67.6862	$67.69	$67.70	$67.70
Purchase #2	$164.26	10.263%	$181.118	$181.12	$181.10	$181.10
Purchase #3	$90.88	13.834%	$103.4523	$103.45	$103.45	$103.50
Purchase #4	$123.98	6.203%	$131.6705	$131.67	$131.65	$131.70
Purchase #5	$188.47	10.311%	$207.9031	$207.90	$207.90	$207.90
Purchase #6	$84.44	6.310%	$89.7682	$89.77	$89.75	$89.80
Purchase #7	$70.54	9.686%	$77.3725	$77.37	$77.35	$77.40
7 purchase totals =	$784.45		$858.9708	$858.97	$858.90	$859.10