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	$153.60	11.597%	$171.413	$171.41	$171.40	$171.40
Purchase #2	$160.37	12.640%	$180.6408	$180.64	$180.65	$180.60
Purchase #3	$72.76	11.300%	$80.9819	$80.98	$81.00	$81.00
Purchase #4	$239.44	11.339%	$266.5901	$266.59	$266.60	$266.60
Purchase #5	$64.32	4.820%	$67.4202	$67.42	$67.40	$67.40
Purchase #6	$104.91	4.817%	$109.9635	$109.96	$109.95	$110.00
Purchase #7	$111.59	4.360%	$116.4553	$116.46	$116.45	$116.50
7 purchase totals =	$906.99		$993.4648	$993.46	$993.45	$993.50