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	$31.99	3.758%	$33.1922	$33.19	$33.20	$33.20
Purchase #2	$42.98	10.284%	$47.4001	$47.40	$47.40	$47.40
Purchase #3	$210.53	5.215%	$221.5091	$221.51	$221.50	$221.50
Purchase #4	$209.62	12.690%	$236.2208	$236.22	$236.20	$236.20
Purchase #5	$178.26	10.296%	$196.6136	$196.61	$196.60	$196.60
Purchase #6	$156.26	4.139%	$162.7276	$162.73	$162.75	$162.70
Purchase #7	$93.28	13.177%	$105.5715	$105.57	$105.55	$105.60
7 purchase totals =	$922.92		$1,003.2349	$1,003.23	$1,003.20	$1,003.20