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	$29.67	7.234%	$31.8163	$31.82	$31.80	$31.80
Purchase #2	$175.31	13.705%	$199.3362	$199.34	$199.35	$199.30
Purchase #3	$110.54	7.573%	$118.9112	$118.91	$118.90	$118.90
Purchase #4	$85.47	3.436%	$88.4067	$88.41	$88.40	$88.40
Purchase #5	$215.40	4.278%	$224.6148	$224.61	$224.60	$224.60
Purchase #6	$165.42	6.666%	$176.4469	$176.45	$176.45	$176.40
Purchase #7	$37.27	8.166%	$40.3135	$40.31	$40.30	$40.30
7 purchase totals =	$819.08		$879.8456	$879.85	$879.80	$879.70