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	$83.31	8.155%	$90.1039	$90.10	$90.10	$90.10
Purchase #2	$78.83	8.532%	$85.5558	$85.56	$85.55	$85.60
Purchase #3	$156.54	5.713%	$165.4831	$165.48	$165.50	$165.50
Purchase #4	$243.75	9.263%	$266.3286	$266.33	$266.35	$266.30
Purchase #5	$42.50	12.869%	$47.9693	$47.97	$47.95	$48.00
Purchase #6	$134.97	6.523%	$143.7741	$143.77	$143.75	$143.80
Purchase #7	$50.27	3.436%	$51.9973	$52.00	$52.00	$52.00
7 purchase totals =	$790.17		$851.2121	$851.21	$851.20	$851.30