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	$49.84	13.117%	$56.3775	$56.38	$56.40	$56.40
Purchase #2	$164.40	13.837%	$187.148	$187.15	$187.15	$187.10
Purchase #3	$135.86	7.259%	$145.7221	$145.72	$145.70	$145.70
Purchase #4	$39.31	7.290%	$42.1757	$42.18	$42.20	$42.20
Purchase #5	$70.99	5.689%	$75.0286	$75.03	$75.05	$75.00
Purchase #6	$124.56	5.830%	$131.8218	$131.82	$131.80	$131.80
Purchase #7	$72.49	13.172%	$82.0384	$82.04	$82.05	$82.00
7 purchase totals =	$657.45		$720.3121	$720.32	$720.35	$720.20