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	$128.43	7.412%	$137.9492	$137.95	$137.95	$137.90
Purchase #2	$220.91	5.171%	$232.3333	$232.33	$232.35	$232.30
Purchase #3	$53.65	10.827%	$59.4587	$59.46	$59.45	$59.50
Purchase #4	$48.38	10.254%	$53.3409	$53.34	$53.35	$53.30
Purchase #5	$13.72	5.720%	$14.5048	$14.50	$14.50	$14.50
Purchase #6	$152.50	8.523%	$165.4976	$165.50	$165.50	$165.50
Purchase #7	$153.32	9.159%	$167.3626	$167.36	$167.35	$167.40
7 purchase totals =	$770.91		$830.4471	$830.44	$830.45	$830.40