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	$94.57	6.642%	$100.8513	$100.85	$100.85	$100.90
Purchase #2	$120.38	6.300%	$127.9639	$127.96	$127.95	$128.00
Purchase #3	$187.90	13.253%	$212.8024	$212.80	$212.80	$212.80
Purchase #4	$143.67	9.245%	$156.9523	$156.95	$156.95	$157.00
Purchase #5	$103.47	6.202%	$109.8872	$109.89	$109.90	$109.90
Purchase #6	$197.63	4.585%	$206.6913	$206.69	$206.70	$206.70
Purchase #7	$90.37	11.238%	$100.5258	$100.53	$100.55	$100.50
7 purchase totals =	$937.99		$1,015.6742	$1,015.67	$1,015.70	$1,015.80