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	$27.75	9.646%	$30.4268	$30.43	$30.45	$30.40
Purchase #2	$208.31	10.164%	$229.4826	$229.48	$229.50	$229.50
Purchase #3	$246.78	3.145%	$254.5412	$254.54	$254.55	$254.50
Purchase #4	$59.71	12.820%	$67.3648	$67.36	$67.35	$67.40
Purchase #5	$75.39	9.367%	$82.4518	$82.45	$82.45	$82.50
Purchase #6	$30.91	13.362%	$35.0402	$35.04	$35.05	$35.00
Purchase #7	$178.78	11.452%	$199.2539	$199.25	$199.25	$199.30
7 purchase totals =	$827.63		$898.5613	$898.55	$898.60	$898.60