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	$103.93	12.686%	$117.1146	$117.11	$117.10	$117.10
Purchase #2	$197.54	10.769%	$218.8131	$218.81	$218.80	$218.80
Purchase #3	$5.72	6.369%	$6.0843	$6.08	$6.10	$6.10
Purchase #4	$19.42	7.374%	$20.852	$20.85	$20.85	$20.90
Purchase #5	$72.91	4.841%	$76.4396	$76.44	$76.45	$76.40
Purchase #6	$82.40	8.436%	$89.3513	$89.35	$89.35	$89.40
Purchase #7	$67.92	7.797%	$73.2157	$73.22	$73.20	$73.20
7 purchase totals =	$549.84		$601.8706	$601.86	$601.85	$601.90