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	$210.55	12.815%	$237.532	$237.53	$237.55	$237.50
Purchase #2	$186.35	13.404%	$211.3284	$211.33	$211.35	$211.30
Purchase #3	$147.30	12.416%	$165.5888	$165.59	$165.60	$165.60
Purchase #4	$104.36	11.298%	$116.1506	$116.15	$116.15	$116.20
Purchase #5	$177.57	3.709%	$184.1561	$184.16	$184.15	$184.20
Purchase #6	$85.69	5.540%	$90.4372	$90.44	$90.45	$90.40
Purchase #7	$53.34	13.355%	$60.4636	$60.46	$60.45	$60.50
7 purchase totals =	$965.16		$1,065.6567	$1,065.66	$1,065.70	$1,065.70