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	$51.40	7.720%	$55.3681	$55.37	$55.35	$55.40
Purchase #2	$102.41	3.303%	$105.7926	$105.79	$105.80	$105.80
Purchase #3	$47.47	7.192%	$50.884	$50.88	$50.90	$50.90
Purchase #4	$82.67	3.447%	$85.5196	$85.52	$85.50	$85.50
Purchase #5	$27.89	7.309%	$29.9285	$29.93	$29.95	$29.90
Purchase #6	$142.75	5.674%	$150.8496	$150.85	$150.85	$150.80
Purchase #7	$179.85	8.539%	$195.2074	$195.21	$195.20	$195.20
7 purchase totals =	$634.44		$673.5498	$673.55	$673.55	$673.50