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	$37.31	7.861%	$40.2429	$40.24	$40.25	$40.20
Purchase #2	$193.44	8.275%	$209.4472	$209.45	$209.45	$209.40
Purchase #3	$59.41	8.550%	$64.4896	$64.49	$64.50	$64.50
Purchase #4	$238.63	10.281%	$263.1636	$263.16	$263.15	$263.20
Purchase #5	$109.87	6.138%	$116.6138	$116.61	$116.60	$116.60
Purchase #6	$65.52	11.682%	$73.174	$73.17	$73.15	$73.20
Purchase #7	$149.66	10.142%	$164.8385	$164.84	$164.85	$164.80
7 purchase totals =	$853.84		$931.9696	$931.96	$931.95	$931.90