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	$66.50	8.334%	$72.0421	$72.04	$72.05	$72.00
Purchase #2	$79.63	8.486%	$86.3874	$86.39	$86.40	$86.40
Purchase #3	$55.29	4.554%	$57.8079	$57.81	$57.80	$57.80
Purchase #4	$19.47	3.799%	$20.2097	$20.21	$20.20	$20.20
Purchase #5	$42.97	6.658%	$45.8309	$45.83	$45.85	$45.80
Purchase #6	$196.81	4.121%	$204.9205	$204.92	$204.90	$204.90
Purchase #7	$29.74	12.758%	$33.5342	$33.53	$33.55	$33.50
7 purchase totals =	$490.41		$520.7327	$520.73	$520.75	$520.60