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	$90.77	9.627%	$99.5084	$99.51	$99.50	$99.50
Purchase #2	$147.43	9.211%	$161.0098	$161.01	$161.00	$161.00
Purchase #3	$96.74	10.254%	$106.6597	$106.66	$106.65	$106.70
Purchase #4	$49.71	3.796%	$51.597	$51.60	$51.60	$51.60
Purchase #5	$193.62	11.308%	$215.5145	$215.51	$215.50	$215.50
Purchase #6	$229.59	10.398%	$253.4628	$253.46	$253.45	$253.50
Purchase #7	$50.88	13.752%	$57.877	$57.88	$57.90	$57.90
7 purchase totals =	$858.74		$945.6292	$945.63	$945.60	$945.70