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	$164.81	3.808%	$171.086	$171.09	$171.10	$171.10
Purchase #2	$245.62	12.292%	$275.8116	$275.81	$275.80	$275.80
Purchase #3	$33.35	6.357%	$35.4701	$35.47	$35.45	$35.50
Purchase #4	$37.41	8.441%	$40.5678	$40.57	$40.55	$40.60
Purchase #5	$219.91	3.861%	$228.4007	$228.40	$228.40	$228.40
Purchase #6	$80.77	10.663%	$89.3825	$89.38	$89.40	$89.40
Purchase #7	$236.82	11.195%	$263.332	$263.33	$263.35	$263.30
7 purchase totals =	$1,018.69		$1,104.0507	$1,104.05	$1,104.05	$1,104.10