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	$33.51	5.870%	$35.477	$35.48	$35.50	$35.50
Purchase #2	$214.93	5.871%	$227.5485	$227.55	$227.55	$227.50
Purchase #3	$47.63	7.640%	$51.2689	$51.27	$51.25	$51.30
Purchase #4	$215.47	8.328%	$233.4143	$233.41	$233.40	$233.40
Purchase #5	$40.44	13.166%	$45.7643	$45.76	$45.75	$45.80
Purchase #6	$189.62	12.362%	$213.0608	$213.06	$213.05	$213.10
Purchase #7	$43.45	12.533%	$48.8956	$48.90	$48.90	$48.90
7 purchase totals =	$785.05		$855.4294	$855.43	$855.40	$855.50