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	$170.33	9.347%	$186.2507	$186.25	$186.25	$186.30
Purchase #2	$53.45	11.294%	$59.4866	$59.49	$59.50	$59.50
Purchase #3	$107.37	4.205%	$111.8849	$111.88	$111.90	$111.90
Purchase #4	$249.41	9.805%	$273.8647	$273.86	$273.85	$273.90
Purchase #5	$178.91	3.797%	$185.7032	$185.70	$185.70	$185.70
Purchase #6	$176.33	6.593%	$187.9554	$187.96	$187.95	$188.00
Purchase #7	$245.56	5.772%	$259.7337	$259.73	$259.75	$259.70
7 purchase totals =	$1,181.36		$1,264.8792	$1,264.87	$1,264.90	$1,265.00