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	$51.44	11.712%	$57.4647	$57.46	$57.45	$57.50
Purchase #2	$245.82	9.209%	$268.4576	$268.46	$268.45	$268.50
Purchase #3	$249.84	8.171%	$270.2544	$270.25	$270.25	$270.30
Purchase #4	$45.89	7.355%	$49.2652	$49.27	$49.25	$49.30
Purchase #5	$82.32	9.243%	$89.9288	$89.93	$89.95	$89.90
Purchase #6	$92.60	8.107%	$100.1071	$100.11	$100.10	$100.10
Purchase #7	$221.80	3.612%	$229.8114	$229.81	$229.80	$229.80
7 purchase totals =	$989.71		$1,065.2892	$1,065.29	$1,065.25	$1,065.40