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	$84.80	7.671%	$91.305	$91.31	$91.30	$91.30
Purchase #2	$250.50	7.622%	$269.5931	$269.59	$269.60	$269.60
Purchase #3	$90.54	8.498%	$98.2341	$98.23	$98.25	$98.20
Purchase #4	$228.78	11.800%	$255.776	$255.78	$255.80	$255.80
Purchase #5	$78.60	8.301%	$85.1246	$85.12	$85.10	$85.10
Purchase #6	$56.81	6.556%	$60.5345	$60.53	$60.55	$60.50
Purchase #7	$83.48	5.827%	$88.3444	$88.34	$88.35	$88.30
7 purchase totals =	$873.51		$948.9117	$948.90	$948.95	$948.80