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	$210.51	12.261%	$236.3206	$236.32	$236.30	$236.30
Purchase #2	$15.88	6.768%	$16.9548	$16.95	$16.95	$17.00
Purchase #3	$178.73	10.115%	$196.8085	$196.81	$196.80	$196.80
Purchase #4	$145.72	7.366%	$156.4537	$156.45	$156.45	$156.50
Purchase #5	$35.37	6.799%	$37.7748	$37.77	$37.75	$37.80
Purchase #6	$60.50	10.871%	$67.077	$67.08	$67.10	$67.10
Purchase #7	$149.43	12.804%	$168.563	$168.56	$168.55	$168.60
7 purchase totals =	$796.14		$879.9524	$879.94	$879.90	$880.10