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	$16.38	10.816%	$18.1517	$18.15	$18.15	$18.20
Purchase #2	$77.27	8.450%	$83.7993	$83.80	$83.80	$83.80
Purchase #3	$116.42	12.789%	$131.309	$131.31	$131.30	$131.30
Purchase #4	$65.78	11.399%	$73.2783	$73.28	$73.30	$73.30
Purchase #5	$89.32	7.494%	$96.0136	$96.01	$96.00	$96.00
Purchase #6	$62.47	3.126%	$64.4228	$64.42	$64.40	$64.40
Purchase #7	$199.74	11.181%	$222.0729	$222.07	$222.05	$222.10
7 purchase totals =	$627.38		$689.0476	$689.04	$689.00	$689.10