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	$62.53	12.813%	$70.542	$70.54	$70.55	$70.50
Purchase #2	$113.57	3.149%	$117.1463	$117.15	$117.15	$117.10
Purchase #3	$80.78	6.320%	$85.8853	$85.89	$85.90	$85.90
Purchase #4	$64.42	4.616%	$67.3936	$67.39	$67.40	$67.40
Purchase #5	$92.25	4.234%	$96.1559	$96.16	$96.15	$96.20
Purchase #6	$37.38	10.172%	$41.1823	$41.18	$41.20	$41.20
Purchase #7	$106.73	5.473%	$112.5713	$112.57	$112.55	$112.60
7 purchase totals =	$557.66		$590.8767	$590.88	$590.90	$590.90