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	$209.42	13.850%	$238.4247	$238.42	$238.40	$238.40
Purchase #2	$97.39	12.270%	$109.3398	$109.34	$109.35	$109.30
Purchase #3	$245.71	9.729%	$269.6151	$269.62	$269.60	$269.60
Purchase #4	$132.81	12.799%	$149.8084	$149.81	$149.80	$149.80
Purchase #5	$100.88	11.873%	$112.8575	$112.86	$112.85	$112.90
Purchase #6	$188.84	5.691%	$199.5869	$199.59	$199.60	$199.60
Purchase #7	$6.80	10.598%	$7.5207	$7.52	$7.50	$7.50
7 purchase totals =	$981.85		$1,087.1531	$1,087.16	$1,087.10	$1,087.10