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	$242.56	5.640%	$256.2404	$256.24	$256.25	$256.20
Purchase #2	$160.95	8.217%	$174.1753	$174.18	$174.20	$174.20
Purchase #3	$106.68	13.215%	$120.7778	$120.78	$120.80	$120.80
Purchase #4	$152.61	9.627%	$167.3018	$167.30	$167.30	$167.30
Purchase #5	$178.70	7.200%	$191.5664	$191.57	$191.55	$191.60
Purchase #6	$37.33	5.744%	$39.4742	$39.47	$39.45	$39.50
Purchase #7	$94.61	6.620%	$100.8732	$100.87	$100.85	$100.90
7 purchase totals =	$973.44		$1,050.4091	$1,050.41	$1,050.40	$1,050.50