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	$152.97	11.123%	$169.9849	$169.98	$170.00	$170.00
Purchase #2	$100.82	6.489%	$107.3622	$107.36	$107.35	$107.40
Purchase #3	$179.98	9.158%	$196.4626	$196.46	$196.45	$196.50
Purchase #4	$236.34	10.326%	$260.7445	$260.74	$260.75	$260.70
Purchase #5	$76.95	8.481%	$83.4761	$83.48	$83.50	$83.50
Purchase #6	$31.89	11.350%	$35.5095	$35.51	$35.50	$35.50
Purchase #7	$46.72	9.783%	$51.2906	$51.29	$51.30	$51.30
7 purchase totals =	$825.67		$904.8304	$904.82	$904.85	$904.90