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	$53.88	9.644%	$59.0762	$59.08	$59.10	$59.10
Purchase #2	$170.59	10.819%	$189.0461	$189.05	$189.05	$189.00
Purchase #3	$71.57	10.326%	$78.9603	$78.96	$78.95	$79.00
Purchase #4	$107.83	11.167%	$119.8714	$119.87	$119.85	$119.90
Purchase #5	$242.94	11.563%	$271.0312	$271.03	$271.05	$271.00
Purchase #6	$95.60	6.347%	$101.6677	$101.67	$101.65	$101.70
Purchase #7	$160.29	4.663%	$167.7643	$167.76	$167.75	$167.80
7 purchase totals =	$902.70		$987.4172	$987.42	$987.40	$987.50