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	$171.92	3.506%	$177.9475	$177.95	$177.95	$177.90
Purchase #2	$54.47	9.872%	$59.8473	$59.85	$59.85	$59.80
Purchase #3	$48.26	6.220%	$51.2618	$51.26	$51.25	$51.30
Purchase #4	$140.77	9.257%	$153.8011	$153.80	$153.80	$153.80
Purchase #5	$82.82	9.289%	$90.5131	$90.51	$90.50	$90.50
Purchase #6	$38.73	10.273%	$42.7087	$42.71	$42.70	$42.70
Purchase #7	$89.54	4.303%	$93.3929	$93.39	$93.40	$93.40
7 purchase totals =	$626.51		$669.4724	$669.47	$669.45	$669.40