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	$67.25	7.689%	$72.4209	$72.42	$72.40	$72.40
Purchase #2	$159.25	6.248%	$169.1999	$169.20	$169.20	$169.20
Purchase #3	$99.84	10.718%	$110.5409	$110.54	$110.55	$110.50
Purchase #4	$192.31	3.718%	$199.4601	$199.46	$199.45	$199.50
Purchase #5	$134.86	5.489%	$142.2625	$142.26	$142.25	$142.30
Purchase #6	$99.83	12.470%	$112.2788	$112.28	$112.30	$112.30
Purchase #7	$156.46	6.655%	$166.8724	$166.87	$166.85	$166.90
7 purchase totals =	$909.80		$973.0355	$973.03	$973.00	$973.10