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	$77.35	7.194%	$82.9146	$82.91	$82.90	$82.90
Purchase #2	$125.43	8.179%	$135.6889	$135.69	$135.70	$135.70
Purchase #3	$101.32	11.779%	$113.2545	$113.25	$113.25	$113.30
Purchase #4	$96.88	8.693%	$105.3018	$105.30	$105.30	$105.30
Purchase #5	$61.28	10.817%	$67.9087	$67.91	$67.90	$67.90
Purchase #6	$10.86	9.596%	$11.9021	$11.90	$11.90	$11.90
Purchase #7	$177.27	6.233%	$188.3192	$188.32	$188.30	$188.30
7 purchase totals =	$650.39		$705.2898	$705.28	$705.25	$705.30