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	$148.88	11.655%	$166.232	$166.23	$166.25	$166.20
Purchase #2	$133.49	12.380%	$150.0161	$150.02	$150.00	$150.00
Purchase #3	$17.94	9.197%	$19.5899	$19.59	$19.60	$19.60
Purchase #4	$189.76	11.785%	$212.1232	$212.12	$212.10	$212.10
Purchase #5	$72.74	7.259%	$78.0202	$78.02	$78.00	$78.00
Purchase #6	$165.57	7.534%	$178.044	$178.04	$178.05	$178.00
Purchase #7	$107.39	3.674%	$111.3355	$111.34	$111.35	$111.30
7 purchase totals =	$835.77		$915.3609	$915.36	$915.35	$915.20