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	$240.44	13.817%	$273.6616	$273.66	$273.65	$273.70
Purchase #2	$136.61	11.751%	$152.663	$152.66	$152.65	$152.70
Purchase #3	$161.27	5.630%	$170.3495	$170.35	$170.35	$170.30
Purchase #4	$177.95	5.461%	$187.6678	$187.67	$187.65	$187.70
Purchase #5	$96.37	9.616%	$105.6369	$105.64	$105.65	$105.60
Purchase #6	$143.51	13.400%	$162.7403	$162.74	$162.75	$162.70
Purchase #7	$185.38	6.188%	$196.8513	$196.85	$196.85	$196.90
7 purchase totals =	$1,141.53		$1,249.5704	$1,249.57	$1,249.55	$1,249.60