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	$46.46	9.275%	$50.7692	$50.77	$50.75	$50.80
Purchase #2	$211.82	7.179%	$227.0266	$227.03	$227.05	$227.00
Purchase #3	$36.84	9.769%	$40.4389	$40.44	$40.45	$40.40
Purchase #4	$78.64	6.327%	$83.6156	$83.62	$83.60	$83.60
Purchase #5	$239.74	9.457%	$262.4122	$262.41	$262.40	$262.40
Purchase #6	$198.35	12.205%	$222.5586	$222.56	$222.55	$222.60
Purchase #7	$48.50	4.706%	$50.7824	$50.78	$50.80	$50.80
7 purchase totals =	$860.35		$937.6035	$937.61	$937.60	$937.60