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	$102.78	13.263%	$116.4117	$116.41	$116.40	$116.40
Purchase #2	$100.75	8.644%	$109.4588	$109.46	$109.45	$109.50
Purchase #3	$196.39	7.179%	$210.4888	$210.49	$210.50	$210.50
Purchase #4	$40.97	8.150%	$44.3091	$44.31	$44.30	$44.30
Purchase #5	$33.93	6.418%	$36.1076	$36.11	$36.10	$36.10
Purchase #6	$228.67	4.479%	$238.9121	$238.91	$238.90	$238.90
Purchase #7	$38.56	11.187%	$42.8737	$42.87	$42.85	$42.90
7 purchase totals =	$742.05		$798.5618	$798.56	$798.50	$798.60