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	$237.73	6.507%	$253.1991	$253.20	$253.20	$253.20
Purchase #2	$36.26	12.766%	$40.889	$40.89	$40.90	$40.90
Purchase #3	$237.98	5.287%	$250.562	$250.56	$250.55	$250.60
Purchase #4	$95.46	8.235%	$103.3211	$103.32	$103.30	$103.30
Purchase #5	$141.96	12.402%	$159.5659	$159.57	$159.55	$159.60
Purchase #6	$104.75	11.372%	$116.6622	$116.66	$116.65	$116.70
Purchase #7	$66.79	6.805%	$71.3351	$71.34	$71.35	$71.30
7 purchase totals =	$920.93		$995.5344	$995.54	$995.50	$995.60