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	$38.48	9.848%	$42.2695	$42.27	$42.25	$42.30
Purchase #2	$150.55	11.728%	$168.2065	$168.21	$168.20	$168.20
Purchase #3	$58.97	10.747%	$65.3075	$65.31	$65.30	$65.30
Purchase #4	$200.72	3.813%	$208.3735	$208.37	$208.35	$208.40
Purchase #5	$160.51	3.732%	$166.5002	$166.50	$166.50	$166.50
Purchase #6	$43.80	6.826%	$46.7898	$46.79	$46.80	$46.80
Purchase #7	$142.75	10.273%	$157.4147	$157.41	$157.40	$157.40
7 purchase totals =	$795.78		$854.8617	$854.86	$854.80	$854.90