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	$96.45	4.158%	$100.4604	$100.46	$100.45	$100.50
Purchase #2	$93.97	12.270%	$105.5001	$105.50	$105.50	$105.50
Purchase #3	$30.56	9.822%	$33.5616	$33.56	$33.55	$33.60
Purchase #4	$123.30	11.851%	$137.9123	$137.91	$137.90	$137.90
Purchase #5	$200.78	4.432%	$209.6786	$209.68	$209.70	$209.70
Purchase #6	$36.37	8.340%	$39.4033	$39.40	$39.40	$39.40
Purchase #7	$120.72	8.804%	$131.3482	$131.35	$131.35	$131.30
7 purchase totals =	$702.15		$757.8645	$757.86	$757.85	$757.90