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	$139.39	12.259%	$156.4778	$156.48	$156.50	$156.50
Purchase #2	$39.52	7.154%	$42.3473	$42.35	$42.35	$42.30
Purchase #3	$154.34	13.811%	$175.6559	$175.66	$175.65	$175.70
Purchase #4	$124.78	7.427%	$134.0474	$134.05	$134.05	$134.00
Purchase #5	$241.27	11.834%	$269.8219	$269.82	$269.80	$269.80
Purchase #6	$170.92	7.793%	$184.2398	$184.24	$184.25	$184.20
Purchase #7	$155.54	10.815%	$172.3617	$172.36	$172.35	$172.40
7 purchase totals =	$1,025.76		$1,134.9518	$1,134.96	$1,134.95	$1,134.90