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	$104.80	4.110%	$109.1073	$109.11	$109.10	$109.10
Purchase #2	$172.78	13.604%	$196.285	$196.29	$196.30	$196.30
Purchase #3	$85.97	12.156%	$96.4205	$96.42	$96.40	$96.40
Purchase #4	$32.66	12.134%	$36.623	$36.62	$36.60	$36.60
Purchase #5	$67.78	5.848%	$71.7438	$71.74	$71.75	$71.70
Purchase #6	$130.96	10.523%	$144.7409	$144.74	$144.75	$144.70
Purchase #7	$168.59	3.387%	$174.3001	$174.30	$174.30	$174.30
7 purchase totals =	$763.54		$829.2206	$829.22	$829.20	$829.10