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	$240.40	7.399%	$258.1872	$258.19	$258.20	$258.20
Purchase #2	$186.40	5.391%	$196.4488	$196.45	$196.45	$196.40
Purchase #3	$23.45	7.654%	$25.2449	$25.24	$25.25	$25.20
Purchase #4	$162.72	5.266%	$171.2888	$171.29	$171.30	$171.30
Purchase #5	$77.84	5.745%	$82.3119	$82.31	$82.30	$82.30
Purchase #6	$28.89	3.253%	$29.8298	$29.83	$29.85	$29.80
Purchase #7	$114.42	8.116%	$123.7063	$123.71	$123.70	$123.70
7 purchase totals =	$834.12		$887.0177	$887.02	$887.05	$886.90