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	$110.78	12.343%	$124.4536	$124.45	$124.45	$124.50
Purchase #2	$62.38	8.690%	$67.8008	$67.80	$67.80	$67.80
Purchase #3	$57.72	5.689%	$61.0037	$61.00	$61.00	$61.00
Purchase #4	$95.78	7.668%	$103.1244	$103.12	$103.10	$103.10
Purchase #5	$226.57	9.649%	$248.4317	$248.43	$248.45	$248.40
Purchase #6	$77.51	12.179%	$86.9499	$86.95	$86.95	$86.90
Purchase #7	$7.95	10.197%	$8.7607	$8.76	$8.75	$8.80
7 purchase totals =	$638.69		$700.5248	$700.51	$700.50	$700.50