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	$178.50	6.258%	$189.6705	$189.67	$189.65	$189.70
Purchase #2	$150.54	12.180%	$168.8758	$168.88	$168.90	$168.90
Purchase #3	$219.60	5.337%	$231.3201	$231.32	$231.30	$231.30
Purchase #4	$85.37	4.354%	$89.087	$89.09	$89.10	$89.10
Purchase #5	$222.29	5.646%	$234.8405	$234.84	$234.85	$234.80
Purchase #6	$47.86	12.703%	$53.9397	$53.94	$53.95	$53.90
Purchase #7	$89.28	5.730%	$94.3957	$94.40	$94.40	$94.40
7 purchase totals =	$993.44		$1,062.1293	$1,062.14	$1,062.15	$1,062.10