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	$81.31	4.616%	$85.0633	$85.06	$85.05	$85.10
Purchase #2	$225.42	4.807%	$236.2559	$236.26	$236.25	$236.30
Purchase #3	$119.26	7.409%	$128.096	$128.10	$128.10	$128.10
Purchase #4	$35.98	11.492%	$40.1148	$40.11	$40.10	$40.10
Purchase #5	$29.71	12.662%	$33.4719	$33.47	$33.45	$33.50
Purchase #6	$65.70	8.696%	$71.4133	$71.41	$71.40	$71.40
Purchase #7	$38.78	12.867%	$43.7698	$43.77	$43.75	$43.80
7 purchase totals =	$596.16		$638.1850	$638.18	$638.10	$638.30