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	$157.77	6.844%	$168.5678	$168.57	$168.55	$168.60
Purchase #2	$240.55	12.868%	$271.504	$271.50	$271.50	$271.50
Purchase #3	$243.39	6.619%	$259.5	$259.50	$259.50	$259.50
Purchase #4	$72.62	7.307%	$77.9263	$77.93	$77.95	$77.90
Purchase #5	$48.46	9.148%	$52.8931	$52.89	$52.90	$52.90
Purchase #6	$123.65	10.717%	$136.9016	$136.90	$136.90	$136.90
Purchase #7	$159.37	7.494%	$171.3132	$171.31	$171.30	$171.30
7 purchase totals =	$1,045.81		$1,138.6060	$1,138.60	$1,138.60	$1,138.60