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	$139.49	4.836%	$146.2357	$146.24	$146.25	$146.20
Purchase #2	$54.98	8.706%	$59.7666	$59.77	$59.75	$59.80
Purchase #3	$242.42	11.763%	$270.9359	$270.94	$270.95	$270.90
Purchase #4	$159.96	7.252%	$171.5603	$171.56	$171.55	$171.60
Purchase #5	$152.58	4.802%	$159.9069	$159.91	$159.90	$159.90
Purchase #6	$104.58	6.221%	$111.0859	$111.09	$111.10	$111.10
Purchase #7	$229.53	7.824%	$247.4884	$247.49	$247.50	$247.50
7 purchase totals =	$1,083.54		$1,166.9797	$1,167.00	$1,167.00	$1,167.00