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	$154.55	7.371%	$165.9419	$165.94	$165.95	$165.90
Purchase #2	$170.78	11.480%	$190.3855	$190.39	$190.40	$190.40
Purchase #3	$28.71	12.559%	$32.3157	$32.32	$32.30	$32.30
Purchase #4	$165.38	5.277%	$174.1071	$174.11	$174.10	$174.10
Purchase #5	$108.42	9.696%	$118.9324	$118.93	$118.95	$118.90
Purchase #6	$121.30	8.276%	$131.3388	$131.34	$131.35	$131.30
Purchase #7	$196.96	5.372%	$207.5407	$207.54	$207.55	$207.50
7 purchase totals =	$946.10		$1,020.5621	$1,020.57	$1,020.60	$1,020.40