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	$38.58	12.556%	$43.4241	$43.42	$43.40	$43.40
Purchase #2	$232.81	4.388%	$243.0257	$243.03	$243.05	$243.00
Purchase #3	$135.97	4.375%	$141.9187	$141.92	$141.90	$141.90
Purchase #4	$86.46	3.443%	$89.4368	$89.44	$89.45	$89.40
Purchase #5	$79.85	7.851%	$86.119	$86.12	$86.10	$86.10
Purchase #6	$59.75	13.840%	$68.0194	$68.02	$68.00	$68.00
Purchase #7	$158.99	13.142%	$179.8845	$179.88	$179.90	$179.90
7 purchase totals =	$792.41		$851.8282	$851.83	$851.80	$851.70