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	$72.38	8.197%	$78.313	$78.31	$78.30	$78.30
Purchase #2	$176.78	13.348%	$200.3766	$200.38	$200.40	$200.40
Purchase #3	$199.54	9.846%	$219.1867	$219.19	$219.20	$219.20
Purchase #4	$249.83	10.716%	$276.6018	$276.60	$276.60	$276.60
Purchase #5	$65.40	6.862%	$69.8877	$69.89	$69.90	$69.90
Purchase #6	$24.97	11.682%	$27.887	$27.89	$27.90	$27.90
Purchase #7	$64.98	3.515%	$67.264	$67.26	$67.25	$67.30
7 purchase totals =	$853.88		$939.5168	$939.52	$939.55	$939.60