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	$31.64	13.799%	$36.006	$36.01	$36.00	$36.00
Purchase #2	$104.38	8.484%	$113.2356	$113.24	$113.25	$113.20
Purchase #3	$90.40	12.147%	$101.3809	$101.38	$101.40	$101.40
Purchase #4	$42.40	9.253%	$46.3233	$46.32	$46.30	$46.30
Purchase #5	$69.37	10.842%	$76.8911	$76.89	$76.90	$76.90
Purchase #6	$183.91	6.655%	$196.1492	$196.15	$196.15	$196.10
Purchase #7	$44.64	11.819%	$49.916	$49.92	$49.90	$49.90
7 purchase totals =	$566.74		$619.9021	$619.91	$619.90	$619.80