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	$91.61	7.776%	$98.7336	$98.73	$98.75	$98.70
Purchase #2	$100.46	5.144%	$105.6277	$105.63	$105.65	$105.60
Purchase #3	$213.39	12.479%	$240.0189	$240.02	$240.00	$240.00
Purchase #4	$216.65	11.814%	$242.245	$242.25	$242.25	$242.20
Purchase #5	$37.45	9.291%	$40.9295	$40.93	$40.95	$40.90
Purchase #6	$142.55	12.825%	$160.832	$160.83	$160.85	$160.80
Purchase #7	$141.68	7.258%	$151.9631	$151.96	$151.95	$152.00
7 purchase totals =	$943.79		$1,040.3498	$1,040.35	$1,040.40	$1,040.20