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	$191.85	9.177%	$209.4561	$209.46	$209.45	$209.50
Purchase #2	$85.54	9.212%	$93.4199	$93.42	$93.40	$93.40
Purchase #3	$238.63	10.570%	$263.8532	$263.85	$263.85	$263.90
Purchase #4	$132.52	10.110%	$145.9178	$145.92	$145.90	$145.90
Purchase #5	$88.35	12.323%	$99.2374	$99.24	$99.25	$99.20
Purchase #6	$43.32	4.124%	$45.1065	$45.11	$45.10	$45.10
Purchase #7	$17.44	8.121%	$18.8563	$18.86	$18.85	$18.90
7 purchase totals =	$797.65		$875.8472	$875.86	$875.80	$875.90