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	$243.62	12.382%	$273.785	$273.79	$273.80	$273.80
Purchase #2	$105.29	3.860%	$109.3542	$109.35	$109.35	$109.40
Purchase #3	$196.90	11.634%	$219.8073	$219.81	$219.80	$219.80
Purchase #4	$96.70	9.737%	$106.1157	$106.12	$106.10	$106.10
Purchase #5	$79.42	8.337%	$86.0412	$86.04	$86.05	$86.00
Purchase #6	$80.75	3.818%	$83.833	$83.83	$83.85	$83.80
Purchase #7	$236.29	5.146%	$248.4495	$248.45	$248.45	$248.40
7 purchase totals =	$1,038.97		$1,127.3859	$1,127.39	$1,127.40	$1,127.30