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	$234.27	6.111%	$248.5862	$248.59	$248.60	$248.60
Purchase #2	$209.85	7.635%	$225.872	$225.87	$225.85	$225.90
Purchase #3	$25.75	6.438%	$27.4078	$27.41	$27.40	$27.40
Purchase #4	$48.81	9.188%	$53.2947	$53.29	$53.30	$53.30
Purchase #5	$82.50	11.542%	$92.0222	$92.02	$92.00	$92.00
Purchase #6	$242.99	13.135%	$274.9067	$274.91	$274.90	$274.90
Purchase #7	$156.66	9.469%	$171.4941	$171.49	$171.50	$171.50
7 purchase totals =	$1,000.83		$1,093.5837	$1,093.58	$1,093.55	$1,093.60