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	$34.68	3.528%	$35.9035	$35.90	$35.90	$35.90
Purchase #2	$48.79	12.554%	$54.9151	$54.92	$54.90	$54.90
Purchase #3	$203.26	10.281%	$224.1572	$224.16	$224.15	$224.20
Purchase #4	$218.26	11.737%	$243.8772	$243.88	$243.90	$243.90
Purchase #5	$231.89	11.456%	$258.4553	$258.46	$258.45	$258.50
Purchase #6	$18.54	13.102%	$20.9691	$20.97	$20.95	$21.00
Purchase #7	$38.31	12.369%	$43.0486	$43.05	$43.05	$43.00
7 purchase totals =	$793.73		$881.3260	$881.34	$881.30	$881.40