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	$6.79	7.484%	$7.2982	$7.30	$7.30	$7.30
Purchase #2	$62.92	3.346%	$65.0253	$65.03	$65.05	$65.00
Purchase #3	$164.45	11.300%	$183.0329	$183.03	$183.05	$183.00
Purchase #4	$90.33	9.839%	$99.2176	$99.22	$99.20	$99.20
Purchase #5	$220.69	10.676%	$244.2509	$244.25	$244.25	$244.30
Purchase #6	$147.72	3.401%	$152.744	$152.74	$152.75	$152.70
Purchase #7	$224.25	7.405%	$240.8557	$240.86	$240.85	$240.90
7 purchase totals =	$917.15		$992.4246	$992.43	$992.45	$992.40