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	$94.80	3.395%	$98.0185	$98.02	$98.00	$98.00
Purchase #2	$67.59	7.472%	$72.6403	$72.64	$72.65	$72.60
Purchase #3	$203.47	9.495%	$222.7895	$222.79	$222.80	$222.80
Purchase #4	$193.98	11.321%	$215.9405	$215.94	$215.95	$215.90
Purchase #5	$79.99	11.703%	$89.3512	$89.35	$89.35	$89.40
Purchase #6	$61.43	12.706%	$69.2353	$69.24	$69.25	$69.20
Purchase #7	$79.62	12.311%	$89.422	$89.42	$89.40	$89.40
7 purchase totals =	$780.88		$857.3973	$857.40	$857.40	$857.30