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	$165.58	3.555%	$171.4664	$171.47	$171.45	$171.50
Purchase #2	$63.39	7.205%	$67.9572	$67.96	$67.95	$68.00
Purchase #3	$88.34	4.231%	$92.0777	$92.08	$92.10	$92.10
Purchase #4	$236.77	7.718%	$255.0439	$255.04	$255.05	$255.00
Purchase #5	$6.32	10.255%	$6.9681	$6.97	$6.95	$7.00
Purchase #6	$74.66	4.599%	$78.0936	$78.09	$78.10	$78.10
Purchase #7	$210.77	10.300%	$232.4793	$232.48	$232.50	$232.50
7 purchase totals =	$845.83		$904.0862	$904.09	$904.10	$904.20