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	$130.86	6.393%	$139.2259	$139.23	$139.25	$139.20
Purchase #2	$118.30	10.498%	$130.7191	$130.72	$130.70	$130.70
Purchase #3	$15.33	9.704%	$16.8176	$16.82	$16.80	$16.80
Purchase #4	$236.68	13.340%	$268.2531	$268.25	$268.25	$268.30
Purchase #5	$40.69	4.672%	$42.591	$42.59	$42.60	$42.60
Purchase #6	$38.60	8.385%	$41.8366	$41.84	$41.85	$41.80
Purchase #7	$85.75	4.226%	$89.3738	$89.37	$89.35	$89.40
7 purchase totals =	$666.21		$728.8171	$728.82	$728.80	$728.80