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	$69.99	10.174%	$77.1108	$77.11	$77.10	$77.10
Purchase #2	$249.54	13.202%	$282.4843	$282.48	$282.50	$282.50
Purchase #3	$225.32	3.582%	$233.391	$233.39	$233.40	$233.40
Purchase #4	$53.69	10.508%	$59.3317	$59.33	$59.35	$59.30
Purchase #5	$66.38	3.796%	$68.8998	$68.90	$68.90	$68.90
Purchase #6	$213.38	5.113%	$224.2901	$224.29	$224.30	$224.30
Purchase #7	$247.72	12.257%	$278.083	$278.08	$278.10	$278.10
7 purchase totals =	$1,126.02		$1,223.5907	$1,223.58	$1,223.65	$1,223.60