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	$161.88	6.166%	$171.8615	$171.86	$171.85	$171.90
Purchase #2	$36.36	7.523%	$39.0954	$39.10	$39.10	$39.10
Purchase #3	$29.55	12.129%	$33.1341	$33.13	$33.15	$33.10
Purchase #4	$90.61	10.165%	$99.8205	$99.82	$99.80	$99.80
Purchase #5	$36.84	7.372%	$39.5558	$39.56	$39.55	$39.60
Purchase #6	$151.70	8.602%	$164.7492	$164.75	$164.75	$164.70
Purchase #7	$242.36	8.792%	$263.6683	$263.67	$263.65	$263.70
7 purchase totals =	$749.30		$811.8848	$811.89	$811.85	$811.90