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	$182.99	4.667%	$191.5301	$191.53	$191.55	$191.50
Purchase #2	$157.98	13.542%	$179.3737	$179.37	$179.35	$179.40
Purchase #3	$90.44	5.631%	$95.5327	$95.53	$95.55	$95.50
Purchase #4	$89.97	6.308%	$95.6453	$95.65	$95.65	$95.60
Purchase #5	$25.33	10.243%	$27.9246	$27.92	$27.90	$27.90
Purchase #6	$89.43	9.854%	$98.2424	$98.24	$98.25	$98.20
Purchase #7	$243.44	12.846%	$274.7123	$274.71	$274.70	$274.70
7 purchase totals =	$879.58		$962.9611	$962.95	$962.95	$962.80