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	$139.83	11.838%	$156.3831	$156.38	$156.40	$156.40
Purchase #2	$244.28	10.831%	$270.738	$270.74	$270.75	$270.70
Purchase #3	$243.46	5.271%	$256.2928	$256.29	$256.30	$256.30
Purchase #4	$6.78	13.787%	$7.7148	$7.71	$7.70	$7.70
Purchase #5	$61.29	13.392%	$69.498	$69.50	$69.50	$69.50
Purchase #6	$152.51	4.102%	$158.766	$158.77	$158.75	$158.80
Purchase #7	$197.34	6.171%	$209.5179	$209.52	$209.50	$209.50
7 purchase totals =	$1,045.49		$1,128.9106	$1,128.91	$1,128.90	$1,128.90