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	$31.59	13.314%	$35.7959	$35.80	$35.80	$35.80
Purchase #2	$189.49	4.743%	$198.4775	$198.48	$198.50	$198.50
Purchase #3	$120.27	13.823%	$136.8949	$136.89	$136.90	$136.90
Purchase #4	$67.34	4.403%	$70.305	$70.31	$70.30	$70.30
Purchase #5	$243.46	12.243%	$273.2668	$273.27	$273.25	$273.30
Purchase #6	$43.37	4.213%	$45.1972	$45.20	$45.20	$45.20
Purchase #7	$156.51	8.456%	$169.7445	$169.74	$169.75	$169.70
7 purchase totals =	$852.03		$929.6818	$929.69	$929.70	$929.70