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	$134.43	5.126%	$141.3209	$141.32	$141.30	$141.30
Purchase #2	$90.96	8.230%	$98.446	$98.45	$98.45	$98.40
Purchase #3	$47.52	11.161%	$52.8237	$52.82	$52.80	$52.80
Purchase #4	$50.35	5.228%	$52.9823	$52.98	$53.00	$53.00
Purchase #5	$141.67	10.504%	$156.551	$156.55	$156.55	$156.60
Purchase #6	$67.56	7.174%	$72.4068	$72.41	$72.40	$72.40
Purchase #7	$7.34	7.367%	$7.8807	$7.88	$7.90	$7.90
7 purchase totals =	$539.83		$582.4114	$582.41	$582.40	$582.40