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	$30.92	8.347%	$33.5009	$33.50	$33.50	$33.50
Purchase #2	$133.46	11.578%	$148.912	$148.91	$148.90	$148.90
Purchase #3	$113.56	10.809%	$125.8347	$125.83	$125.85	$125.80
Purchase #4	$167.28	4.449%	$174.7223	$174.72	$174.70	$174.70
Purchase #5	$226.36	5.392%	$238.5653	$238.57	$238.55	$238.60
Purchase #6	$72.79	8.229%	$78.7799	$78.78	$78.80	$78.80
Purchase #7	$205.50	3.535%	$212.7644	$212.76	$212.75	$212.80
7 purchase totals =	$949.87		$1,013.0795	$1,013.07	$1,013.05	$1,013.10