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	$221.57	7.538%	$238.2719	$238.27	$238.25	$238.30
Purchase #2	$81.34	3.674%	$84.3284	$84.33	$84.35	$84.30
Purchase #3	$50.43	11.835%	$56.3984	$56.40	$56.40	$56.40
Purchase #4	$59.48	12.267%	$66.7764	$66.78	$66.80	$66.80
Purchase #5	$246.77	11.264%	$274.5662	$274.57	$274.55	$274.60
Purchase #6	$17.88	12.156%	$20.0535	$20.05	$20.05	$20.10
Purchase #7	$93.48	6.411%	$99.473	$99.47	$99.45	$99.50
7 purchase totals =	$770.95		$839.8678	$839.87	$839.85	$840.00