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	$19.26	5.489%	$20.3172	$20.32	$20.30	$20.30
Purchase #2	$118.47	11.849%	$132.5075	$132.51	$132.50	$132.50
Purchase #3	$30.33	3.604%	$31.4231	$31.42	$31.40	$31.40
Purchase #4	$180.25	8.364%	$195.3261	$195.33	$195.35	$195.30
Purchase #5	$46.38	7.749%	$49.974	$49.97	$49.95	$50.00
Purchase #6	$139.47	7.820%	$150.3766	$150.38	$150.40	$150.40
Purchase #7	$96.56	13.822%	$109.9065	$109.91	$109.90	$109.90
7 purchase totals =	$630.72		$689.8310	$689.84	$689.80	$689.80