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	$108.83	3.732%	$112.8915	$112.89	$112.90	$112.90
Purchase #2	$85.99	5.498%	$90.7177	$90.72	$90.70	$90.70
Purchase #3	$250.41	7.406%	$268.9554	$268.96	$268.95	$269.00
Purchase #4	$98.52	13.872%	$112.1867	$112.19	$112.20	$112.20
Purchase #5	$89.81	4.830%	$94.1478	$94.15	$94.15	$94.10
Purchase #6	$86.81	9.504%	$95.0604	$95.06	$95.05	$95.10
Purchase #7	$92.77	12.686%	$104.5388	$104.54	$104.55	$104.50
7 purchase totals =	$813.14		$878.4983	$878.51	$878.50	$878.50