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	$136.69	4.740%	$143.1691	$143.17	$143.15	$143.20
Purchase #2	$65.34	9.641%	$71.6394	$71.64	$71.65	$71.60
Purchase #3	$147.42	12.245%	$165.4716	$165.47	$165.45	$165.50
Purchase #4	$35.57	11.658%	$39.7168	$39.72	$39.70	$39.70
Purchase #5	$217.72	3.677%	$225.7256	$225.73	$225.75	$225.70
Purchase #6	$246.62	7.744%	$265.7183	$265.72	$265.70	$265.70
Purchase #7	$73.55	11.502%	$82.0097	$82.01	$82.00	$82.00
7 purchase totals =	$922.91		$993.4505	$993.46	$993.40	$993.40