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	$36.69	3.334%	$37.9132	$37.91	$37.90	$37.90
Purchase #2	$239.63	6.380%	$254.9184	$254.92	$254.90	$254.90
Purchase #3	$245.75	7.126%	$263.2621	$263.26	$263.25	$263.30
Purchase #4	$36.26	11.153%	$40.3041	$40.30	$40.30	$40.30
Purchase #5	$91.30	13.829%	$103.9259	$103.93	$103.95	$103.90
Purchase #6	$163.26	13.757%	$185.7197	$185.72	$185.70	$185.70
Purchase #7	$234.91	10.495%	$259.5638	$259.56	$259.55	$259.60
7 purchase totals =	$1,047.80		$1,145.6072	$1,145.60	$1,145.55	$1,145.60