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	$85.31	5.521%	$90.02	$90.02	$90.00	$90.00
Purchase #2	$244.86	9.537%	$268.2123	$268.21	$268.20	$268.20
Purchase #3	$5.98	7.835%	$6.4485	$6.45	$6.45	$6.40
Purchase #4	$131.81	11.692%	$147.2212	$147.22	$147.20	$147.20
Purchase #5	$169.53	12.759%	$191.1603	$191.16	$191.15	$191.20
Purchase #6	$136.61	7.469%	$146.8134	$146.81	$146.80	$146.80
Purchase #7	$219.43	10.267%	$241.9589	$241.96	$241.95	$242.00
7 purchase totals =	$993.53		$1,091.8346	$1,091.83	$1,091.75	$1,091.80