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	$25.58	6.872%	$27.3379	$27.34	$27.35	$27.30
Purchase #2	$204.74	13.871%	$233.1395	$233.14	$233.15	$233.10
Purchase #3	$180.82	8.468%	$196.1318	$196.13	$196.15	$196.10
Purchase #4	$29.69	9.315%	$32.4556	$32.46	$32.45	$32.50
Purchase #5	$42.68	6.757%	$45.5639	$45.56	$45.55	$45.60
Purchase #6	$211.41	4.399%	$220.7099	$220.71	$220.70	$220.70
Purchase #7	$87.78	6.668%	$93.6332	$93.63	$93.65	$93.60
7 purchase totals =	$782.70		$848.9718	$848.97	$849.00	$848.90