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	$172.58	7.599%	$185.6944	$185.69	$185.70	$185.70
Purchase #2	$210.36	3.811%	$218.3768	$218.38	$218.40	$218.40
Purchase #3	$109.79	8.842%	$119.4976	$119.50	$119.50	$119.50
Purchase #4	$74.94	4.238%	$78.116	$78.12	$78.10	$78.10
Purchase #5	$195.67	7.558%	$210.4587	$210.46	$210.45	$210.50
Purchase #6	$195.31	9.362%	$213.5949	$213.59	$213.60	$213.60
Purchase #7	$247.48	6.874%	$264.4918	$264.49	$264.50	$264.50
7 purchase totals =	$1,206.13		$1,290.2302	$1,290.23	$1,290.25	$1,290.30