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	$229.59	13.824%	$261.3285	$261.33	$261.35	$261.30
Purchase #2	$174.38	8.536%	$189.2651	$189.27	$189.25	$189.30
Purchase #3	$148.30	12.345%	$166.6076	$166.61	$166.60	$166.60
Purchase #4	$27.34	10.800%	$30.2927	$30.29	$30.30	$30.30
Purchase #5	$129.48	7.432%	$139.103	$139.10	$139.10	$139.10
Purchase #6	$136.96	13.164%	$154.9894	$154.99	$155.00	$155.00
Purchase #7	$136.98	11.633%	$152.9149	$152.91	$152.90	$152.90
7 purchase totals =	$983.03		$1,094.5012	$1,094.50	$1,094.50	$1,094.50