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	$223.94	6.663%	$238.8611	$238.86	$238.85	$238.90
Purchase #2	$120.39	13.812%	$137.0183	$137.02	$137.00	$137.00
Purchase #3	$208.79	11.314%	$232.4125	$232.41	$232.40	$232.40
Purchase #4	$161.33	10.671%	$178.5455	$178.55	$178.55	$178.50
Purchase #5	$101.33	8.227%	$109.6664	$109.67	$109.65	$109.70
Purchase #6	$87.90	9.590%	$96.3296	$96.33	$96.35	$96.30
Purchase #7	$28.33	13.143%	$32.0534	$32.05	$32.05	$32.10
7 purchase totals =	$932.01		$1,024.8868	$1,024.89	$1,024.85	$1,024.90