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	$101.63	12.103%	$113.9303	$113.93	$113.95	$113.90
Purchase #2	$40.41	8.413%	$43.8097	$43.81	$43.80	$43.80
Purchase #3	$190.82	6.846%	$203.8835	$203.88	$203.90	$203.90
Purchase #4	$86.96	3.379%	$89.8984	$89.90	$89.90	$89.90
Purchase #5	$127.96	7.614%	$137.7029	$137.70	$137.70	$137.70
Purchase #6	$171.40	11.427%	$190.9859	$190.99	$191.00	$191.00
Purchase #7	$61.33	3.542%	$63.5023	$63.50	$63.50	$63.50
7 purchase totals =	$780.51		$843.7130	$843.71	$843.75	$843.70