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	$66.51	8.431%	$72.1175	$72.12	$72.10	$72.10
Purchase #2	$78.54	13.361%	$89.0337	$89.03	$89.05	$89.00
Purchase #3	$106.66	8.353%	$115.5693	$115.57	$115.55	$115.60
Purchase #4	$78.97	3.860%	$82.0182	$82.02	$82.00	$82.00
Purchase #5	$60.57	6.736%	$64.65	$64.65	$64.65	$64.70
Purchase #6	$217.77	13.615%	$247.4194	$247.42	$247.40	$247.40
Purchase #7	$141.89	6.231%	$150.7312	$150.73	$150.75	$150.70
7 purchase totals =	$750.91		$821.5393	$821.54	$821.50	$821.50