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	$137.46	7.514%	$147.7887	$147.79	$147.80	$147.80
Purchase #2	$64.87	11.323%	$72.2152	$72.22	$72.20	$72.20
Purchase #3	$237.98	10.349%	$262.6086	$262.61	$262.60	$262.60
Purchase #4	$169.69	9.488%	$185.7902	$185.79	$185.80	$185.80
Purchase #5	$132.78	7.317%	$142.4955	$142.50	$142.50	$142.50
Purchase #6	$40.40	7.529%	$43.4417	$43.44	$43.45	$43.40
Purchase #7	$90.90	8.168%	$98.3247	$98.32	$98.30	$98.30
7 purchase totals =	$874.08		$952.6646	$952.67	$952.65	$952.60