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	$80.29	3.235%	$82.8874	$82.89	$82.90	$82.90
Purchase #2	$101.33	10.179%	$111.6444	$111.64	$111.65	$111.60
Purchase #3	$35.90	9.312%	$39.243	$39.24	$39.25	$39.20
Purchase #4	$140.53	8.541%	$152.5327	$152.53	$152.55	$152.50
Purchase #5	$123.34	8.364%	$133.6562	$133.66	$133.65	$133.70
Purchase #6	$222.44	12.606%	$250.4808	$250.48	$250.50	$250.50
Purchase #7	$26.26	4.782%	$27.5158	$27.52	$27.50	$27.50
7 purchase totals =	$730.09		$797.9603	$797.96	$798.00	$797.90