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	$59.87	8.200%	$64.7793	$64.78	$64.80	$64.80
Purchase #2	$227.43	5.553%	$240.0592	$240.06	$240.05	$240.10
Purchase #3	$29.52	12.751%	$33.2841	$33.28	$33.30	$33.30
Purchase #4	$146.97	7.149%	$157.4769	$157.48	$157.50	$157.50
Purchase #5	$37.35	13.604%	$42.4311	$42.43	$42.45	$42.40
Purchase #6	$205.48	9.163%	$224.3081	$224.31	$224.30	$224.30
Purchase #7	$92.48	7.624%	$99.5307	$99.53	$99.55	$99.50
7 purchase totals =	$799.10		$861.8694	$861.87	$861.95	$861.90