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	$28.36	10.487%	$31.3341	$31.33	$31.35	$31.30
Purchase #2	$110.36	12.507%	$124.1627	$124.16	$124.15	$124.20
Purchase #3	$42.43	10.812%	$47.0175	$47.02	$47.00	$47.00
Purchase #4	$222.77	12.608%	$250.8568	$250.86	$250.85	$250.90
Purchase #5	$238.77	13.667%	$271.4027	$271.40	$271.40	$271.40
Purchase #6	$182.59	6.315%	$194.1206	$194.12	$194.10	$194.10
Purchase #7	$157.39	5.792%	$166.506	$166.51	$166.50	$166.50
7 purchase totals =	$982.67		$1,085.4004	$1,085.40	$1,085.35	$1,085.40