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	$28.48	3.308%	$29.4221	$29.42	$29.40	$29.40
Purchase #2	$60.41	3.156%	$62.3165	$62.32	$62.30	$62.30
Purchase #3	$219.51	7.637%	$236.274	$236.27	$236.25	$236.30
Purchase #4	$72.46	13.731%	$82.4095	$82.41	$82.40	$82.40
Purchase #5	$135.45	8.547%	$147.0269	$147.03	$147.05	$147.00
Purchase #6	$155.48	5.689%	$164.3253	$164.33	$164.35	$164.30
Purchase #7	$150.96	11.558%	$168.408	$168.41	$168.40	$168.40
7 purchase totals =	$822.75		$890.1823	$890.19	$890.15	$890.10