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	$53.93	7.338%	$57.8874	$57.89	$57.90	$57.90
Purchase #2	$71.84	4.755%	$75.256	$75.26	$75.25	$75.30
Purchase #3	$57.38	13.837%	$65.3197	$65.32	$65.30	$65.30
Purchase #4	$223.31	3.564%	$231.2688	$231.27	$231.25	$231.30
Purchase #5	$147.76	13.312%	$167.4298	$167.43	$167.45	$167.40
Purchase #6	$200.74	12.408%	$225.6478	$225.65	$225.65	$225.60
Purchase #7	$6.73	4.655%	$7.0433	$7.04	$7.05	$7.00
7 purchase totals =	$761.69		$829.8528	$829.86	$829.85	$829.80