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	$5.55	6.219%	$5.8952	$5.90	$5.90	$5.90
Purchase #2	$65.59	8.419%	$71.112	$71.11	$71.10	$71.10
Purchase #3	$51.33	6.554%	$54.6942	$54.69	$54.70	$54.70
Purchase #4	$101.69	10.291%	$112.1549	$112.15	$112.15	$112.20
Purchase #5	$64.28	7.627%	$69.1826	$69.18	$69.20	$69.20
Purchase #6	$69.29	13.705%	$78.7862	$78.79	$78.80	$78.80
Purchase #7	$5.50	9.243%	$6.0084	$6.01	$6.00	$6.00
7 purchase totals =	$363.23		$397.8335	$397.83	$397.85	$397.90