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	$91.54	9.134%	$99.9013	$99.90	$99.90	$99.90
Purchase #2	$37.81	6.229%	$40.1652	$40.17	$40.15	$40.20
Purchase #3	$33.33	6.511%	$35.5001	$35.50	$35.50	$35.50
Purchase #4	$163.56	6.601%	$174.3566	$174.36	$174.35	$174.40
Purchase #5	$159.52	8.143%	$172.5097	$172.51	$172.50	$172.50
Purchase #6	$176.72	5.353%	$186.1798	$186.18	$186.20	$186.20
Purchase #7	$5.57	11.223%	$6.1951	$6.20	$6.20	$6.20
7 purchase totals =	$668.05		$714.8078	$714.82	$714.80	$714.90